Ok, here is my best build to date.  This was a sound quality build, and I was not going for SPL.  Before I get to the pics (of which I only have a few), I'll give you a full description.
 
The platform was my 1993 Honda Accord LX.  I started by completely removing the interior and laying down a layer of Dynamat on the entire car from the floor boards to the doors, and trunk.  I then ran the power and RCA cables.  I chose a 0 gauge cable for both power and ground, and in order to ensure that there would never be any grounding issue or engine whine in the system, I welded the ground cable to the frame directly.  The power cable ran back to an Alumapro 15 farad capacitor/distribution block which allowed me to run short power cables to all of the additional components using 8 gauge cable.
 

 
The source Unit was a Pioneer P9300

running to an Audio Control Three.1 in dash EQ and Preout amplifier which allowed for adjustment of the preouts all the way up to 7v.
 

Then the signal ran back to the trunk to a Pheonix Gold MX3i 3 way electronic Crossover.
 

 
Then the signal was split in 3 directions.  The high pass signal was sent to one of two Audio Control EQT 31 band 1/3 octave equalizers.  One for the left channel, and one for the right channel.  These had to be adjusted using an RTA (Real Time Analyzer) because the human ear has a hard time distinguishing between each of the 31 frequencies that can be adjusted. 
 

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From each of the EQ's the signal then ran to a McIntosh MC440M which was bi-amped for only the front stage.  Bi-amp means that I used one channel to power a tweeter, and one channel to power a midbass driver in the door per side.  Total of 4 channels with no rear speakers.
 
 
 
This McIntosh provided amplification for my pair of Hifonics Zeus series 6.5 in seperates.  The 6.5 in. midbass drivers were mounted in the doors which had been sealed in with Dynamat to create an enclosure for the speakers, and the tweeters were fiberglassed into the A-pillars in order to bring the sound stage up higher.
 

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Now back to the Pheonix Gold MX3i.  The signal was also sent in a third direction from here to an Arc Audio 2100CXL 2 channel amp which powered my sub.
 

 
And finally to my subwoofer.  A single Image Dynamics IDQ15 mounted in the spare tire well.
 

 
Here is my finished product.
 

 

 

 
Nice mods @ tweaked. Lookin good man!
 
Just wanted to share pics of my car pc installation inside the dash of my VW Jetta-



 

 

 

 

  Below - The GPU has been overclocked from a stock setting of 650Mhz, to a nice and stable 774Mhz @ 32c.

 

Veloci Raptor for the OS, and 1.5 TB of ripped digital audio tracks in CDA quality + DVD video in the glove box bolted under the PC.

 

 
Below...a 320 watt DC to DC power supply powers the PC without any DC to AC inverters...
 

 
A five-port, 32 in one multi-media card reader mounted above for easy access file transfers....

here it is while in use..

 
Now this is what the PC looks like when the top black, air vent cover is removed. The computer housing is fabricated out of highly polished aluminum diamond plate...

 

 
High speed wireless broadband from clearwire...

 
connects to my magic jack for mobile telephone service.

I use this wireless remote to dial the telephone numbers...

 

 
with mic audio running through the web cam

 
and then in to the SB X-Fi Fatality Professional...

 
• Equipped with 64 megabytes of X-RAM,
performance is increased over motherboard audio by up to 15%,
delivering the most intense bone crushing lows and crisp highs.

• Total Harmonic Distortion 0.0008% @ -3dB
• Frequency Response: 10Hz to 96kHz
• 24-bit Digital-to-Analog conversion:
• 96kHz to analog 7.1 speaker output

You'll hear everything in crystal clarity when tethered to a Pioneer Premier MultiMedia Controller, like this one below, at 4 X 50 watts. It takes the ultra crisp signals from the sound blaster on steroids, and rattles the temperature gauge inside my firmly planted rear view mirror.

 
Both rear seats fold down...seatbacks are trimmed with diamond plate and an amp is mounted on each side....

 
22" LCD display recessed in the door...

It's had more than two years of abuse with door slamming closed- No problems at all.

The monitor is secured inside with 1/4 in aluminum plate and bolted to the door with tamper proof torx.

Playing Crysis Warhead while waiting on the wife to do her shopping at the mall.

 
Or my thirteen year old daughter can sing karaoke choosing amongst over 10,000 songs as we wait in the car...

 

 

 
Watch HDTV over the air, or through the ClearWire wireless broadband connection.

 

 

 

 
Staggered sized 22's TSW Kayalami's adorn the outside

with a body kit painted to match.
 

@davey That is one of the most amazing things I have ever seen man.  Truely impressive.  How long did it take you to get everything put in, set up and working.  Also if a problem were to come up how hard would it be to work on and fix it?

Kingandruler

@davey That is one of the most amazing things I have ever seen man.  Truely impressive.  How long did it take you to get everything put in, set up and working.  Also if a problem were to come up how hard would it be to work on and fix it?

Thank you. It took me a few weeks of careful planning on paper before I started doing the installation. The motherboard is a microATX platform from ShuttlePC; model ST20-G5, it has a Dual core AMD 2.2Ghz processor w/ 4GB of ram.
 
It has never given me any problems from constant road vibration because the cards are hot glued to the slots and so are all the power connectors as they went in. Disassembly may take a while but I've not had to do that yet. :)
Toughest part of the build was trying to make everything theft proof. I can stand on top of the lcd mounted to the door, and shake the whole car. The pc won't come out in one piece till the entire dash is removed.
 
Nevertheless, the power supply is designed specifically for AT, ATX, uATX, FlexATX, Mini ITX motherboards for mobility. When you switch off the ignition the PC can go into shut down, standby or hibernate modes automatically. It has a micro-controller that controls and monitors various functions of the power supply operation. It monitors vehicle battery voltage to protect against deep discharge. The ignition lead is monitored to start the PC when the ignition is turned on and to implement safe shutdown procedure. It controls and monitors motherboard signals to provide smooth power-up and power-down sequences even while the engine is being started. The power supply can be configured to shut down the PC after a predetermined delay of up to 60 min. The outputs are monitored to assure proper PC operation.

Wake on interrupt feature in DC-DC together with Wake on LAN function on motherboards can be used to access the vehicle/mobile PC over wireless network without turning on the ignition switch for up to 20 min. at a time. This feature is useful for updating, uploading and down loading data/files of the car PC remotely. A green LED indicator in the power supply continually indicates the status and health. It is also used for troubleshooting.
 
The entire project took almost 6 months to complete as I didn't want to rush and miss something along the way. The motherboard has served me well. Nevertheless, I am thinking about replacing it with a zotac h55-itx, the processor will be an i5-655K with 8GB ram, and a few SSD's.
 
 

I know there are more car audio guys out there!  Lets see those systems.

Tweaked

Wow Davey!  So what prompted that kind of work?  Just for the fun of it, or were you trying to build a show car?

I love music and clarity was what I aimed for but didn't like switching out cd's often. Besides, I had the parts laying around collecting dust. 

Wow Davey that is some wicked stuff you got there... crazy!

A friend of mine has a really simple system in his truck, just a 500w amp and 2x 10inch kicker subs... Ill post a picture if i can get/find one

bump this back up. lets see some systems. Ive got pics coming of the new setup soon :)

and here i am with a crappy aftermarket pioneer head unit hooked to 4 250W rms 6 1/2 speakers in an altima... miss my navigators system >_<

Ill get some build pics up soon but heres a teaser.

@Eppo
 
That is a beast Amp you got there, Also what sub is that on the left?

@rush
Sundown nightshade 15 dual 2ohm. Wired down at 1 ohm in a 3.5 cu box tuned at 28hz made of 1.5 inch birch and fiberglassed for strength.
Amp is a sundown 3k, does 3000 watts of clean power @ 12v. Closer to 3400 at 14.4
 
Car- 2010 Mazdaspeed3 
Sub- 15 inch Sundown Nightshade V1
Amp- Sundown 3k
Headunit- AVH-4400bh
Front battery- Diehard Platnium 34
Rear Battery- Kinetik HC800 x 2 (soon to be replaced with 2 c&d 140ah)
Wire- 2 runs of 1/0 SHOK CCA, Big3/Grounds - Kicker Hyperflex 1/0
 
Gotta have a couple fuses panels built, a set of batt terminals, and some dual 1/0 to 1/0 stud adapters.
Also want to rebuild the box to 33hz with aeroports.

Wow...that's a lot of work..and far more than I'd care to put in...I'm happy with my factory stuff (I can't hear the difference anymore, honestly...)
 

Here is my temporary, its made to play high db and still needs the last finish;