nFans are becoming more and more necessary for modern computers.  They're used to simply move air through the computer or cool specific components.  What more people should realize is that not all fans are the same, and it is a wise choice to select high quality fans that last long, fit your noise tolerance and provide enough airflow for your needs.  In this thread I'll make recommendations on fans to choose from, but first lets go over some terms you should know.

Terms and Abbreviations

RPM - Revolutions per minute.  Measure of the complete rotations completed by the motor hub/fan blades.  The higher the RPM, the more air movement but noise also increases.  A more powerful motor is needed to achieve high RPM reliably, therefore motor noise might also increase.

CFM - Cubic feet per minute.  Measure of the speed of air movement.  Higher means more airflow, but increased RPM leads to increased CFM, therefore higher CFM fans will also be more noisy.  The design and amount of fan blades affects CFM as well.

DBA - Decibels.  Measure of noise.  Higher is louder.  Here is a useful sound chart.

Static Pressure - Measured air pressure.  Commonly overlooked.  Higher static pressure means the fan can output air that can more easily overcome the resistance to airflow.  High pressure fans are especially ideal for fans installed on heat sinks or radiators, since the air will be forced through the fins and heat pipes more easily.

Undervolting - Reducing voltage to the fan via a fan controller to lower fan speed.  Fans that undervolt well emit a normal fan noise, while fans that don't undervolt well make odd sounds and pitches.  

Sizes

Computer fans come in a variety of sizes.  The most used sizes include 40mm, 60mm, 80mm, 92mm and 120mm.  140mm fans are becoming more common as well, and some companies offer even larger fans such as 180mm, 200mm, 220mm, 230mm or 250mm.  The thickness of most 60mm-140mm fans is 25mm, but some exceptions include the extra high pressure 38mm thick fans and there are some other rare exceptions.  The larger fans tend to be slightly more thick.

Smaller fans have to spin faster in order to create more airflow, while larger fans can spin at a lower speed and still provide adequate airflow and much less noise.  Over time you will have your own preferred fan sizes.

Bearings

The bearings of a fan is also important.  These affect motion between the moving parts inside of the fan.  Here is an overview of commonly used bearings in computer fans.  The following information has been taken from wikipedia, and I added my own modifications and information.

Sleeve Bearings - Features two surfaces lubricated with oil or grease as a friction contact. Sleeve bearings are less durable as the contact surfaces can become rough and/or the lubricant dry up, eventually leading to failure. Sleeve bearings may be more likely to fail at higher temperatures, and may perform poorly when mounted in any orientation other than vertical. The lifespan of a sleeve bearing fan may be around 40,000 hours at 40 °C. Fans that use sleeve bearings are generally cheaper than fans that use ball bearings, and are quieter at lower speeds early in their life, but can grow considerably noisier as they age.
 
Rifle Bearings - Similar to sleeve bearings, but are quieter and have almost as much lifespan as ball bearings. The bearing has a spiral groove in it that pumps fluid from a reservoir. This allows them to be safely mounted horizontally (unlike sleeve bearings), since the fluid being pumped lubricates the top of the shaft. The pumping also ensures sufficient lubricant on the shaft, reducing noise, and increasing lifespan.
 
Ball Bearings - Though generally more expensive, ball bearing fans do not suffer the same orientation limitations as sleeve bearing fans, are more durable especially at higher temperatures, and quieter than sleeve bearing fans at higher rotation speeds. The lifespan of a ball bearing fan may be around 63,000 hours at 40 °C. Some fans use one ball bearing, some use two and some use one ball and one sleeve. The latter is cheaper and less effective.
 
Fluid Dynamic Bearings - These have the advantages of near-silent operation and higher life expectancy than even ball bearing fans, due to the lack of contact with the shaft, bearing and thrust plate. However, these fans tend to be the most expensive.
 
Magnetic Bearings - The fan is repelled from the bearing by magnetism. Stabilizes the rotor axis. Noctua's Self-Stabilizing Oil Pressure Bearing (SSO Bearing) is a fluid dynamic bearing with a magnet. 
 
Fan Blade Designs

Many computer fans have a different fan blade design so I'll list the more noticeable ones.  Different blade designs are not just done for aesthetic reasons or to be unique - the design of the fan blades can severely affect CFM, static pressure and even noise level to some extent.

You will see only a few things vary with different blade designs.  The number of blades as well as the curve/direction of the blades.  You will also see a difference in space between each blade.  Adding more fan blades can result in more air movement, but if they're too close together you'll end up with less air movement.  Thicker/wider blades are good at directing air straight forward, for better static pressure.  This is also the reason most fan blades are curved.

Triple Blade Design - Used on nearly every house fan or non computer fan, but some computer fans use it too such as Delta EEB fans and their 120mm x 76mm fan.  To be honest, I couldn't tell you why this design is ever used.  The three blades are usually curved a lot so that they can actually move a decent amount of air in a more straight path.  But these three blades obviously have to revolve faster to be as effective as a fan with more blades, so these are more noisy and have limited performance.  Skip fans with this blade design.



Wide Blade Design - Many computer fans have seven blades but are widespread so that there is less of a gap in between them.  You can see this design used on most Sanyo Denki and Panaflo fans.  This design allows for greater static pressure and doesn't limit airflow much so it's a great design.



Wavy Blade Design - Every now and then you'll come across a computer fan with wavy blades.  Cooler Master's BladeMaster fans use this design, and so do Enermax fans.  This design forces air in a straight pattern, improving static pressure, and due to the gap between the blades a good amount of air is being moved as well.  Overall it is a good design.



Directional Fan Blades - Some fans have integrated grills attached to the back of them, behind the fan blades.  The most effective ones are known as directional fan blades - these are counter-spun to the fan blades, directing the air straight forward.  Delta and Nidec were probably the first manufacturers to offer computer fans with this design.  Silverstone has a slightly altered design on their Air Penetrator fans.

Most fans with this design have more directional fan blades than fan blades, but this can limit airflow.  Delta introduced the PFB series which offer 11 fan blades and 9 directional fan blades.  These happen to be their best fans, offering the highest static pressure and CFM.  Airflow is less restricted since there are more fan blades than directional fan blades, and the added fan blades improved static pressure compared to their older fans.

Silverstone's Air Penetrator fans have seven fan blades and a very dense integrated grill which is counter-spun to the fan blades.  As a result, there is an improvement in air direction.  Air is moved more straight than other fans.  But the grill is awfully restricted so CFM takes a big hit.  This isn't as much of an issue on the AP181 and AP141 due to their larger size and RPM.  But the AP121 suffers from this, judging by its 36 CFM rating.  Most people are better off skipping the AP121, but the AP141 and AP181 are very useful fans.



Fan Placement

Putting fans in random spots in your computer is not going to help.  You want fans to intake air from somewhere, preferably outside of the case and from other fans that intake air from outside of the case.  You also want fans that exhaust air out of the case.  For more information on preferred airflow methods, please have a look at my Airflow Guide.

I will go over different types of air pressures encountered in computers, although my airflow guide also goes over them. 

Negative Air Pressure - Negative air pressure is probably the most common. It should really be avoided. In order to have negative air pressure, you must have more exhaust power than intake power. As a result, air is passively drawn in through open slots and ventilation. This would bring in more dust, and make it harder for video cards to exhaust air since the flow of air is going against it.
 
Positive Air Pressure - Positive air pressure is not as common in computer cases, but it is a preferred method of cooling. In a positive air pressure system, you must have more intake power than exhaust power. As a result, air passively leaves the case through open slots and ventilation. This reduces the amount of dust in the case, and it makes it easier for video cards to exhaust air since the flow of air is going with it.

Neutral Air Pressure - Neutral air pressure means you have equal intake power and exhaust power.  In a neutral air pressure system, there is less air passively moving into and out of the case.  This causes a lack of air movement in some areas of the case, sometimes causing hot spots, or places where heat builds up.
Brand Names

Some brand names offer a large selection of high quality fans, earning them a recommendation and a spot on the following list.

Delta - Best choice for ridiculously awesome cooling with no noise tolerance.  High end server grade fans.
Nidec - They manufacture Scythe GentleTyphoons and other great fans that can be found on some power supplies (Antec Signature series).   They manufacture very high end server grade fans.
Noctua - A tad overpriced, but excellent quality fans with one of the best bearing designs around.
Panaflo - Great mix of airflow, pressure and low noise with very good quality.
Sanyo Denki - Known for great undervolting and low noise compared to others in the price range.  Very high end, server grade.      
Scythe - GentleTyphoon series are their best but the S-Flex and similar fans are also good.  Avoid their "Kaze" and "Slipstream" fans - see below for reasons. 
Thermalright - FDB series = rebranded Scythe S-Flex so they're good.  
Xigmatek - Good budget fans
Yate Loon - Good budget fans

Of course there are exceptions, but the above brand names are some of the best either in quality or price to performance, some of those rock both of those worlds.

Recommended Websites
You're most likely going to order your fans online, but visiting your local Fry's or Microcenter is a good idea.  The following websites have a nice selection of fans (among other products) and don't scam you.
CrazyPC
FrozenCPU
Newegg
Performance-PCs
PetrasTechShop - If you want Yate Loons, come here first
Sidewinder Computers

Of course there are other good sites to choose from, but these are the sites I mainly use.

Fan Recommendations

Now that the basic information is covered, I can now make a list of fans I recommend in the given sizes and price ranges.  Also, the fans listed here are actually easy to find.  Remember - 38mm thick fans are mostly recommended for heat sinks and radiators.  Lets work our way up.

40mm Fans

Delta EFB0412HA - 40mm x 40mm x 10mm, 6000 RPM/6.92 CFM/28.5 DBA, 3-pin power connector, ball bearing.
Delta AFB0412LB - 40mm x 40mm x 15mm, 5000 RPM/6.5 CFM/18.5 DBA, 3-pin power connector, ball bearing.
Delta FFB0412MN - 40mm x 40mm x 28mm, 5000 RPM/8.05 CFM/23.9 DBA, 3-pin power connector, ball bearing.  Delta FFB0412VHN - 40mm x 40mm x 28mm, 9500 RPM/15.79 CFM/41.9 DBA, 3-pin power connector, ball bearing.  Delta FFB0412SHN - 40mm x 40mm x 28mm, 13000 RPM/24 CFM/51.5 DBA, 3-pin power connector, ball bearing.  Delta GFB0412EHS - 40mm x 40mm x 56mm, 16200 RPM/26.92 CFM/62.5 DBA, 3-pin power connector, dual ball bearings.
Panaflo FBK04F12U - 40mm x 40mm x 20mm, 9500 RPM/9.2 CFM/42 DBA, 3-pin power connector, hydro wave bearing.

60mm Fans

Delta AFB0612HH - 60mm x 60mm x 25mm, 5000 RPM/27.55 CFM/40 DBA, 3-pin power connector, ball bearing.
Delta AFB0612SH - 60mm x 60mm x 25mm, 6000 RPM/34.15 CFM/44.5 DBA, 10.73 mmH20 static pressure, 3-pin power connector, ball bearing.
Delta AFB0612EH - 60mm x 60mm x 25mm, 6800 RPM/36.35 CFM/46.5 DBA, 3-pin power connector, ball bearing.
Panaflo L1 Ultra Quiet FBA06A12L - 60mm x 60mm x 25mm, 3200 RPM/14.1 CFM/24 DBA, 3-pin power connector, hydro wave bearing.
Panaflo HL High Performance FBA06A12H - 60mm x 60mm x 25mm, 4200 RPM/19.1 CFM/32 DBA, 3-pin power connector, hydro wave bearing.  

80mm x 80mm x 25mm Fans

Panaflo L1 Ultra Quiet FBA08A12L - 1900 RPM/24 CFM/21 DBA, 3-pin power connector, hydro wave bearing.
Panaflo M1 Performance FBA08A12M - 2450 RPM/32.1 CFM/28 DBA, 3-pin power connector, hydro wave bearing.
Panaflo H1 High Performance FBA08A12H - 2950 RPM/39.6 CFM/32 DBA, 3-pin power connector, hydro wave bearing.
Panaflo U1 Ultra Performance FBA08A12U - 3450 RPM/46.9 CFM/38.2 DBA, 3-pin power connector, hydro wave bearing.
Scythe Kama Flow2 SP0825FDB12L - 1400 RPM/18.97 CFM/14 DBA, 3-pin power connector w/ 4-pin adapter, fluid dynamic bearing.
Scythe Kama Flow2 SP0825FDB12M - 2200 RPM/30.67 CFM/25.9 DBA, 3-pin power connector w/ 4-pin adapter, fluid dynamic bearing.
Scythe Kama Flow2 SP0825FDB12H - 2900 RPM/39.96 CFM/32.2 DBA, 3-pin power connector w/ 4-pin adapter, fluid dynamic bearing.  
Scythe S-Flex SFF80B - 1500 RPM/21.5 CFM/12.2 DBA, 3-pin power connector w/ 4-pin adapter, fluid dynamic bearing.
Scythe S-Flex SFF80C - 2000 RPM/28.7 CFM/20 DBA, 3-pin power connector w/ 4-pin adapter, fluid dynamic bearing.
Scythe S-Flex SFF80D - 2800 RPM/40.2 CFM/32.4 DBA, 3-pin power connector w/ 4-pin adapter, fluid dynamic bearing.
Yate Loon Low Speed D80SL-12 - 2000 RPM/25 CFM/26 DBA, 3-pin power connector, sleeve bearings.  Great cheap fan.
Yate Loon Medium Speed D80SM-12 - 2200 RPM/27 CFM/29 DBA, 3-pin power connector, sleeve bearings.  Great cheap fan.

80mm x 80mm x 38mm Fans

Delta TFB0812UHE - 8000 RPM/106.26 CFM/65 DBA, 3-pin power connector, ball bearing.
Delta PFB0812UHE - 7500 RPM/107.30 CFM/61 DBA, 3-pin power connector, ball bearing.  
Vantec TD8038H - 5700 RPM/84.1 CFM/55.2 DBA, 3-pin power connector w/ 4-pin adapter, dual ball bearings. 

92mm x 92mm x 25mm Fans

Delta AFB0912L - 1800 RPM/37.25 CFM/25 DBA, 3-pin power connector, ball bearing.  
Delta AFB0912SH - 4800 RPM/102.59 CFM/53 DBA, 3-pin power connector, ball bearing.  
Delta FFB0912SH - 4100 RPM/90.02 CFM/50 DBA, 3-pin power connector, ball bearing.
Noctua NF-B9 - 1600 RPM/37.8 CFM/19.8 DBA, 3-pin power connector w/ 4-pin adapter, SSO bearing.
Panaflo Ultra Quiet FBA09A12L1BX - 2100 RPM/42.7 CFM/27 DBA, 3-pin power connector, hydro wave bearing.
Panaflo Medium Speed FBA09A12M1BX - 2450 RPM/48 CFM/30 DBA, 3-pin power connector, hydro wave bearing.
Panaflo High Speed FBA09A12H1BX - 2850 RPM/56.8 CFM/35 DBA, 3-pin power connector, hydro wave bearing.
Sanyo Denki San Ace 109P0912M401 - 2100 RPM/36.7 CFM/27 DBA, 3-pin power connector, ball bearing.  
Scythe GentleTyphoon D0925C12B1AP-12 - 1700 RPM/25 CFM/13 DBA, 3-pin power connector w/ 4-pin adapter, dual ball bearings.
Scythe GentleTyphoon D0925C12B1AP-13 - 2150 RPM/34 CFM/20 DBA, 3-pin power connector w/ 4-pin adapter, dual ball bearings.  
Scythe GentleTyphoon D0925C12B1AP-14 - 2650 RPM/41 CFM/26 DBA, 3-pin power connector w/ 4-pin adapter, dual ball bearings.  
Scythe Kama Flow2 SP0925FDB12L - 1200 RPM/21.39 CFM/16.9 DBA, 3-pin power connector w/ 4-pin adapter, fluid dynamic bearing.  
Scythe Kama Flow2 SP0925FDB12M - 1700 RPM/30.31 CFM/24.4 DBA, 3-pin power connector w/ 4-pin adapter, fluid dynamic bearing.  
Scythe Kama Flow2 SP0925FDB12H - 2200 RPM/40.32 CFM/29.5 DBA, 3-pin power connector w/ 4-pin adapter, fluid dynamic bearing.  
Scythe S-Flex SFF92A - 1000 RPM/21.6 CFM/9.4 DBA, 3-pin power connector w/ 4-pin adapter, fluid dynamic bearing.
Scythe S-Flex SFF92B - 1500 RPM/32.4 CFM/17.4 DBA, 3-pin power connector w/ 4-pin adapter, fluid dynamic bearing.
Scythe S-Flex SFF92C - 2000 RPM/43.2 CFM/25.3 DBA, 3-pin power connector w/ 4-pin adapter, fluid dynamic bearing.
Scythe S-Flex SFF92D - 2500 RPM/54 CFM/33.3 DBA, 3-pin power connector w/ 4-pin adapter, fluid dynamic bearing. 
 
92mm x 92mm x 38mm Fans

Delta TFB0912GHE - 5400 RPM/126.48 CFM/59.2 DBA, 3-pin power connector, ball bearing.
Delta TFB0912UHE - 6000 RPM/142.20 CFM/62 DBA, 3-pin power connector, ball bearing.
Delta PFB0912DHE - 8000 RPM/175.03 CFM/66.5 DBA, 3-pin power connector, ball bearing.
Vantec TD9238H - 4800 RPM/119 CFM/56.4 DBA, 3-pin power connector w/ 4-pin adapter, dual ball bearings. 

120mm x 120mm x 25mm Fans

Delta FFB1212EH - 4000 RPM/150.33 CFM/56.4 DBA, 3-pin power connector, ball bearing.
Noctua NF-P12 - 1300 RPM/54.3 CFM/19.8 DBA, 3-pin power connector w/ 4-pin adapter, SSO bearing (magnetic fluid bearing).
Noctua NF-F12 - 1500 RPM/55 CFM/22.4 DBA, 2.61 mmH2O static pressure, 4-pin PWM connector, SSO2 bearing (magnetic fluid bearing)
Sanyo Denki San Ace 9S1212H4011 - 2700 RPM/86.5 CFM/36 DBA, 4.572 mmH20 static pressure, 3-pin power connector, ball bearing.  
Sanyo Denki San Ace 9G1212H4011 - 2850 RPM/88 CFM/40 DBA, 6.5278 mmH20 static pressure, 3-pin power connector, ball bearing.
Scythe GentleTyphoon D1225C12B1AP-11 - 500 RPM/18 CFM/5 DBA, 3-pin power connector w/ 4-pin adapter, dual ball bearings.
Scythe GentleTyphoon  D1225C12B2AP-12 - 800 RPM/28 CFM/9 DBA, 3-pin power connector w/ 4-pin adapter, dual ball bearings.
Scythe GentleTyphoon D1225C12B2AP-13 - 1150 RPM/37 CFM/16 DBA, 3-pin power connector w/ 4-pin adapter, dual ball bearings. 
Scythe GentleTyphoon D1225C12B2AP-14 - 1450 RPM/50 CFM/21 DBA, 1.2954 mmH20 static pressure, 3-pin power connector w/ 4-pin adapter, dual ball bearings.  Scythe Webpage
Scythe GentleTyphoon D1225C12B2AP-15 - 1850 RPM/57 CFM/28 DBA, 2.0574 mmH20 static pressure, 3-pin power connector w/ 4-pin adapter, dual ball bearings.  Scythe Webpage
Scythe GentleTyphoon D1225C12B6AP-0A - 2150 RPM/69 CFM/30 DBA, 2.8702 mmH20 static pressure
Scythe GentleTyphoon D1225C12B7AP-29 - 3000 RPM/83 CFM/36.5 DBA, 5.08 mmH20 static pressure, 4-pin PWM connector, dual ball bearings.  
Scythe GentleTyphoon D1225C12B9AP-30 - 4250 RPM/116.5 CFM/44 DBA, 9.652 mmH20 static pressure, 4-pin PWM connector, dual ball bearings.   
Scythe GentleTyphoon D1225C12BBAP-31 - 5400 RPM/150 CFM/50.5 DBA, 15.24 mmH20 static pressure, 4-pin PWM connector, dual ball bearings. 
Thermalright TR-FDB-800 - 800 RPM/30.5 CFM/13.1 DBA, 3-pin power connector, fluid dynamic bearing.
Thermalright TR-FDB-1000 - 1000 RPM/38.9 CFM/15.8 DBA, 3-pin power connector, fluid dynamic bearing.
Thermalright TR-FDB-1300 - 1300 RPM/50 CFM/24.1 DBA, 3-pin power connector, fluid dynamic bearing.
Thermalright TR-FDB-1600 - 1600 RPM/63.7 CFM/28 DBA, 3-pin power connector, fluid dynamic bearing.
Thermalright TR-FDB-2000 - 2000 RPM/80.5 CFM/37 DBA, 3-pin power connector, fluid dynamic bearing.
Xigmatek XSF-F1251 - 1800 RPM/72 CFM/24 DBA, 3-pin power connector, one ball bearing and one sleeve bearing.  Good cheap fan.
Yate Loon Low Speed D12SL-12 - 1350 RPM/47 CFM/28 DBA, 3-pin power connector w/ 4-pin adapter, sleeve bearings.  Good cheap fan.
Yate Loon Medium Speed D12SM-12 - 1650 RPM/70.5 CFM/33 DBA, 3-pin power connector w/ 4-pin adapter, sleeve bearings.  Good cheap fan.
Yate Loon High Speed D12SH-12 - 2200 RPM/88 CFM/40 DBA, 3-pin power connector w/ 4-pin adapter, sleeve bearings.  Good cheap fan.

120mm x 120mm x 38mm Fans

Delta FFB1212EHE - 4000 RPM/190 CFM/59 DBA, 3-pin power connector, ball bearing.
Delta TFB1212GHE - 4600 RPM/220.01 CFM/65 DBA, 26.44 mmH20 static pressure, 3-pin power connector, ball bearing.
Delta PFB1212GHE - 4800 RPM/217.8 CFM/62 DBA, 27.308 mmH20 static pressure, 3-pin power connector, ball bearing.
Delta PFB1212UHE - 5500 RPM/252.85 CFM/66.5 DBA, 35.877 mmH20 static pressure, 3-pin power connector, ball bearing.
Panaflo L1 Low Noise FBA12G12L - 1700 RPM/68.9 CFM/30 DBA, 3-pin power connector, hydro wave bearing.
Panaflo M1 Medium Volume FBA12G12M-1BX - 2100 RPM/86.5 CFM/35 DBA, 3-pin power connector, hydro wave bearing.
Panaflo H1 High Speed FBA12G12H1BX - 2500 RPM/103.8 CFM/41.5 DBA, 3-pin power connector, hydro wave bearing.
Panaflo U1 Ultra High Speed FBA12G12U - 2705 RPM/114.7 CFM/45.5 DBA, 3-pin power connector, hydro wave bearing.
Sanyo Denki San Ace 9G1212H1011 - 2600 RPM/99 CFM/39 DBA, 7.1882 mmH20 static pressure, 3-pin power connector, ball bearing.  

140mm Fans

The only fans here are 140mm x 140mm x 25mm fans, with one exception.  This is because it's almost impossible to obtain 140mm x 140mm x 38mm fans.  So obviously 120mm fans are better for high performance cooling, and overall there are more high end 120mm fans than there are 140mm fans.

Noctua NF-A14 - 140mm x 140mm x 25mm square fan, 1500 RPM/82.5 CFM/24.6 DBA, 2.08 mmH2O static pressure, SSO2 bearing (magnetic fluid bearing).
Noctua NF-A15 - 150mm x 140mm x 25mm round fan, 1200 RPM/68 CFM/19.2 DBA, 1.51 mmH2O static pressure, SSO2 bearing (magnetic fluid bearing)
Thermalright TY-141 - 152mm x 140mm x 26.5mm round fan, 1300 RPM/73.6 CFM/21 DBA, dual ball bearing
Thermalright TY-143 - 152mm x 140mm x 26.5mm round fan, 2500 RPM/130 CFM/45 DBA (PWM, can go down as low as 600 RPM), 45 DBA
Thermalright TY-147 - 152mm x 140mm x 26.5mm round fan, 1300 RPM/73.6 CFM/21 DBA, enhanced hyper-flow bearing (high quality fluid bearing)
Thermalright TY-150 - 160mm x 140mm x 26.5mm round fan, 1100 RPM/84.2 CFM/34 DBA, dual ball bearing
Silverstone AP-141 - 140mm x 140mm x 25mm square fan, 1500 RPM/64.34 CFM/30.1 DBA, 1.55 mmH2O static pressure, fluid bearing
Yate Loon D14SL-12 - 1000 RPM/46.9 CFM/25 DBA, 3-pin power connector w/ 4-pin adapter, sleeve bearings.  Good cheap fan.
Yate Loon D14SM-12 - 1400 RPM/62 CFM/29 DBA, 3-pin power connector w/ 4-pin adapter, sleeve bearings.  Good cheap fan.
 
How To Acquire Delta, Nidec and Sanyo Denki Fans
 
Delta, Nidec and Sanyo Denki are some of the very best fan manufacturers and the best choices for extremely powerful cooling.  You can find some of their fans at the websites listed above, but for high prices and it's still a limited selection.  So how do you go about acquiring these fans?  You will have to buy them from industrial suppliers instead.  They sell a wide variety of Delta, Nidec and Sanyo Denki fans for lower prices than you'd expect.  They're the best choices for bulk orders.  The downsides?  No connectors are typically present.  Just the sheathed wires so you'll have to add the connectors yourself.
 

• OnlineComponents - Excellent supplier for Delta fans.
• MPJA - Variety of rare fans, best site I've found for Nidec fans.
• Newark - They have tons of Sanyo Denki fans.  To simplify and shorten your search, click here for a list of 120mm x 25mm fans, here are their 120mm x 38mm fans, here are their 140mm fans and you can find other, odd sized Sanyo Denki fans such as 150mm and 172mm.  

So there you have it.  If you have a case with those large 200+mm fans, you're better off swapping them out for multiple 120mm fans or even 140mm fans.  Doing this will not only provide better airflow, but also remain just as silent if you choose your fans wisely, and improve lifespan since there are no high quality 200+mm fans.  Silverstone 180mm fans are pretty good - particularly the FM-181 which is the only one with ball bearings.  But their AP181 fan is even better despite using sleeve bearings.  The sleeve bearings are modified so that they don't perform badly in a horizontal position.  Their air penetrator fans have a grill on them to direct air.  This impedes air movement drastically but improves direction.  Here is a review on the AP181 fans.
 
Why You Should Avoid Scythe Slipstreams and Scythe Ultra Kazes
 
These fans are popular due to their low price and high CFM rating.  But they're cheap for a reason.  SlipStreams are just terrible fans.  Why?  Here is a list.
 
- Sleeve Bearings - You can see the downsides to these at the top of the post.
- Poor Static Pressure - Making it a poor choice for heat sinks and radiators.  Yate Loon 120mm high speeds do a much better job at cooling, as you'll see in the links below.  And Yate Loons cost even less.
- Cheap Build Quality - The motor is designed for 80mm fans.  This contributes to a short lifespan.  The motor will crap out before the sleeve bearings will.
- Horrible Undervolting - When undervolted, they'll make loud clicking noises and/or whining which is just annoying, and they don't stay within RPM specification.
 
The Ultra Kazes have the same issues, minus the build quality issues.  They're not horribly built.  But they undervolt terribly, have sleeve bearings and poor pressure of only about 3 mmH20 (San Ace 120mm x 25mm fans have more pressure at a lower RPM).
 
Here are some links you should look at, even after looking at this guide.

"The Well Dressed Megahalems - A test of 65 fans and 112 fan setups on a Prolimatech Megahalems heat sink.
Jab Tech Yates vs Petras Yates
Fan Testing
XtremeSystems Fan Review
My Airflow Guide
List of Recommended Cases
My CPU Air Cooling Guide
Anatomy of the Silent Fan
 
Special thanks to Yerbuddy for making me realize a thread like this should be made.

Excellent post boredgunner!  Just a quick question, I'm about to install a Corsair H70. I've also purchased a couple Scythe GT-15's. Based on your thread, would I benefit in replacing the stock fans with the Scythes and then using the stock H70 fans on top of my HAF 932 and remove the 230mm fan. I think the 230mm has 110cfm. Maybe two fans wouldn't help out. Not sure....

yes sticky please

boredgunner, appreciate the info. i'll swap out the h70 stock for the 230mm and see how that works out. thanks!

Go for the Delta.  Their fans are top quality.   Much better specs than the Rexus.

your sidewinder computers link takes you to a site about the snake 

lol, now worries i did that more than once when i first found out about the site 

i HIGHLY HIGHLY HIGHLY x100000 Would suggest against Peformance-PC as your shopping source - when i had done business with them, over $1000 worth of products, they decided they would rather lose a customer than RMA and replace a bad product - they LITERALLY SAID TO ME - i asked my boss and he said he doesnt agree and would rather just lose the customer, when i replied and asked why the hell he would rather take that route - they responded with - "well, we've kinda already over-saturated the market"   so basically this company would rather give you the finger than good service...
 
BUT i have to give GREAT Credit to their managers and workers, who saw this was just WRONG and didnt agree with their boss and made sure to take care of me under the radar.... So things got solved, but the boss wanted to just screw me and make me reorder that $100 defunctional product from another vendor...
 
Really pissed me off at first, was just mind blown when i saw the final result.... companies like this should be shut down and their managers (the ones im speaking about that solved the problem) should own their own shop, i find it fkin SICK that companies work like this, look at NewEgg - atleast they keep quality customer service no matter how large they are....
 
NEWEGG FOR THE WIN! (and no im not a newegg worker/promoter, ive just never had a problem with them that wasnt solved Extreemly quickly and even given discounts for random problems that can be applied to my next order ect... i LOVE newegg...)
 

I believe these are the stock H70 fans.  Your best bet would be to ask Corsair or ask on their forums though.
 
http://www.newegg.com/Product/Product.aspx?Item=N82E16835200048&cm_re=rosewill_120mm-_-35-200-048-_-Product
 
They're decent performers but not the most quiet.  Some guy here swapped out the stock fans for a pair of Scythe GentleTyphoon AP-15s and got around the same temps but much less noise.  These will do what you wish... perform better without a noticeable noise increase, if any.  30 DBA for the stock fans is hard to believe considering they're 2000 RPM sleeve bearing fans...
 
http://www.newegg.com/Product/Product.aspx?Item=N82E16835705002&cm_re=panaflo_120mm-_-35-705-002-_-Product

boredgunner

I believe these are the stock H70 fans.  Your best bet would be to ask Corsair or ask on their forums though.

http://www.newegg.com/Product/Product.aspx?Item=N82E16835200048&cm_re=rosewill_120mm-_-35-200-048-_-Product

They're decent performers but not the most quiet.  Some guy here swapped out the stock fans for a pair of Scythe GentleTyphoon AP-15s and got around the same temps but much less noise.  These will do what you wish... perform better without a noticeable noise increase, if any.  30 DBA for the stock fans is hard to believe considering they're 2000 RPM sleeve bearing fans...

http://www.newegg.com/Product/Product.aspx?Item=N82E16835705002&cm_re=panaflo_120mm-_-35-705-002-_-Product

 
Ah, finally dug something up!
 

Two fans are supplied with the H70 and are 120x120x25mm models. These fans are rated for 1600-2000RPM operation and this can be selected by the user through installation of the two step down adapters which are bundled with the unit. Corsair rates the fans at 50.35-61.2 CFM, 1.8-2.3mm H20 static pressure (each) and 26-31.5dBA of noise per fan. Each fan has a 3-pin connector and Corsair supply a cable to power these off a single 3-pin motherboard connector.

 
http://www.hardwareheaven...review-the-cooler.html
 
So they do actually give the static pressure on these (take the high numbers, I haven't throttled them.)
 
It looks like the Rosewill you linked to is quite similar but with a little more amperage to drive it; thus a slightly higher CFM. I'd imagine against a rad the extra 0.1 amps would keep the static pressure up a bit. Nice call.
 
The fan you linked to as a recommendation looks like it would do the trick - but the fact that it's 38mm vs 25mm is tough going because then I'd need brand new screws to mount them to the rad and case. The screws the Corsair H70 uses are much longer (little more than an inch or so) and thinner diameter (by perhaps 1/3) than the usual fan screws.
 
Anyway, thanks for input on this. I'll stop the threadjack! This is a great post. Well done!

boredgunner

Meh, I don't consider it to be threadjacking.  Cooler Master BladeMasters (120mm x 25mm) actually have a static pressure rating of nearly 4 mmH20.  Those H70 fans have poor pressure if I do say so myself.  The thing is, the BladeMasters won't necessarily be quieter.  They too are 2000 RPM sleeve bearing fans.  However Cooler Master should be releasing their hydrostatic bearing BladeMasters - the ones included with the V6 and V6 GT.  But where are they...

The San Ace 9G1212H4011 (120mm x 25mm) has a 40 DBA rating with a static pressure of over 6 mmH20 if you're interested.

http://www.performance-pcs.com/catalog/index.php?main_page=product_info&cPath=36_49&products_id=27970

 
Now we're talking. I'll have to see what Santa brings me for Christmas... if there's cash involved, this might be something I pickup!

check the info on the sythe fans,i have 3 of them 120x38 they worked great for the first 3 months,now i am junking them.temps have risen.do not know if it is the fans or my house temps.but it was hotter in the summer.

boredgunner

patchesanook

check the info on the sythe fans,i have 3 of them 120x38 they worked great for the first 3 months,now i am junking them.temps have risen.do not know if it is the fans or my house temps.but it was hotter in the summer.

Dust build up would be my first guess.  I have one of these coming tomorrow.  It will be used on my Thermalright Shaman.  I'm eager to hear it.  I expected my Panaflo U1 120mm to sound loud but my GTX 480's stock cooler is much louder.  That fan coming tomorrow has a similar DBA rating.  

 
"It also has an amazing near 3:1 airflow to noise ratio."
 
best quote ever for a fan...

boredgunner

Okay guys, I just had to share this with you.  Dual ball bearing Nidec fan, crazy performance, insane build quality.  $13.50.

http://www.goldmango.com/19612.html

What do you guys think about that site though? 

geek32 

nice info!!! 

wish there would be slim case fans like 120mmx12mm with LEDS.  would like the scythe slim fans but they don't have LEDS or colors hehe 

 

Useful in some scenarios yeah.  There are some new 120mm x 25mm LED fans out on the market.  Silverstone AP121s now have LEDs.

http://silverstonetek.com/products/p_contents.php?pno=AP121-L&area=

They have also released the AP141.  I'm liking the CFM rating compared to the AP121.  Static pressure is slightly lower but I have use for one... or two.

http://silverstonetek.com/products/p_contents.php?pno=AP141&area=

 
oh i love those air penetrator fans.  gonna buy those if they sell on newegg.  thanks for sharing.

Glad to help and nice choice.  Added a section on fan blade design to the OP.  I ordered that Nidec VA450DC nice and smooth.  $13.50 + $8 shipping.  Can't wait.  My first > 64 DBA fan!