It's very possible in that price range to make an AMAZING computer.
I'll update this post with an edit and make a few suggestions in a few minutes.
I did this build up very quickly.
Someone may be able to come up with a better one.
- Free shipping w/ promo code EMCYPYN48, ends 3/8
The total comes to $814 if you use the shipping promo code.
With... $45 worth of rebates.
Basically my suggestion for a good graphics card that could potentially last 3 years and run modern games smooth as butter...
ATI Radeon HD 5850
It will stomp all over any existing Nvidia card. (That's less than $500)
I suggest going with AMD over Intel right now because the gaming performance is similar and Thuban's just around the corner.
(And it saves money)
The Rosewill Blackbone is an amazing case for the price. (I'd rate it 10/10)
I forgot OS and Optical Drive, if you absolutely need those things you can bump the CPU down to a Phenom II X4 925, or a Phenom II X3 720, or Phenom II X2 555.
The Phenom II X4 955 is a great quad core processor geared for overclocking. (Unlocked multiplier)
The PSU will last you and run the rig just fine. (OCZ, 80+ certified, lots of Amps on the 12v rails, what more could you ask for?)
The RAM is DDR3 1600Mhz with CL8 timings, good stuff.
The Hard Drive was a budget choice on my part.
Seagate's not known for having the fastest or most reliable, but right now for it's price bracket that 500Gb sure is a good deal.