I'm putting this list together because it seems the 400 series is gaining in popularity because of the relatively low cost and great performance they offer. This is to help you prospective 400 series shoppers determine what you'll be looking at in terms of a PSU to feed them.
 
As with my other thread, I'll be referencing a site that uses the same system with the same specs for measurements so they can be comparable. Please note numbers observed are for the entire system at peak loads.
 
4x GTX480 SLI = 1188w
http://www.guru3d.com/art...-gtx-4way-sli-review/8
 
3x GTX480 SLI = 1009w
http://www.guru3d.com/art...480-3way-sli-review/25
 
2x GTX480 SLI = 702w
http://www.guru3d.com/art...480-3way-sli-review/25
 
1x GTX480 = 419w
http://www.guru3d.com/art...480-3way-sli-review/25
 
3x GTX470 SLI = 794w
http://www.guru3d.com/art...-2-3-way-sli-review/23
 
2x GTX470 SLI = 567w
http://www.guru3d.com/art...-2-3-way-sli-review/23
 
1x GTX470 = 411w
http://www.guru3d.com/art...-2-3-way-sli-review/23
 
(note: they didn't thoroughly test a multiple GPU GTX465 SLI system. However as you can see a single GTX465 consumes roughly 60w less than a GTX470 system. So we can safely assume what powers a 2x, 3x SLI GTX470 system will be fine for GTX465's)
 
1x GTX465 = 342w
http://www.guru3d.com/art...ce-gtx-465-sc-review/5
 
2x GTX460 SLI = 433w
http://www.guru3d.com/art...-gtx-460-sli-review/15
 
1x GTX460 = 307w 
http://www.guru3d.com/art...orce-gtx-460-review/13
 
2x GTS450 = 402w
http://www.guru3d.com/art...-gts-450-sli-review/14
 
1x GTS450  = 275w
http://www.guru3d.com/art...-gts-450-sli-review/14
 
Also concerning the numbers above, it is generally a good idea to give yourself about 100w or so of head room with your PSU. So for instance if the setup you're looking at requires 702w like for instance the SLI GTX480 system. You'll want to have at least a 800 - 850w PSU.
 
One final note guys, please remember that the quality of your PSU matters greatly. Don't go buy some cheap Apevia 1000w PSU and think you're good to go. The reality is that those cheap PSUs aren't what they are cracked up to be. Often times they are severely overrated 700w units or even less. The way companies rate PSUs is a bit deceptive. Often times they will rate them for their maximum load and not their continuous load. A PSU that is rated for 1000w max is not able to sustain that load for any real length of time and will most likely fail if asked to do so. Maximum load ratings are only for load spikes or short term. A PSU that is rated for a continuous output is capable of delivering that wattage for any length of time for the operational lifetime of the PSU.
 
Just remember that cheap = cheap, never cut corners on your PSU. This doesn't mean go buy the biggest and highest current PSU you can get. This means simply to buy from trusted and reputable brands like Antec, Seasonic, Sliverstone, Enermax, Ultra, Corsair, PC Power & Cooling and a few others.

Thanks AB