Building new gaming PC

Copro,
Mmmm, spending $500 on the listed Tom's System will get you a decent gaming experiance, using 1 monitor on average settings. You'll probably want to upgrade the CPU at a later date if things get too "laggy" with whatever games come out in the future. And, it may last you 3 years, but newer games always place the largest demand on PC's. In 3 years another $500-750 will get you a much faster machine without fail.
grafxfx
 
The EA-380D is a solid PSU, BUT if you want to play BF3, it may take more than a $500 PC to play it well. Take a look at the more recent $500 SBM machine as well. It contains a stronger GPU, which should help. Read the discussions after both build articles for ideas on improvements; both could really benefit from another $100 or so.
 
No reason to upgrade the PSU unless you plan on expanding this PC in the future. If you look at the power consumption charts you'll see that their build only drew 180W. I have the Antec Earthwatts 380, and I've read some reviews on it and it is a solid PSU.

The only thing I'd really suggest based on that build (while keeping the price the same) is getting one of the 6850's that have good rebates going. You can get an overclocked XFX for ~$130. Then take the money saved and upgrade the motherboard and get DDR3-1600 RAM.

Or, the other option is to get a 6870 since those can be had for $170.