Budget Gamer ($330 Core Total):
AMD Athlon 64 X2 5200+ 2.6GHz 2MB ($130)
2GB DDR2-800 4-4-4 ($80)
GeForce 8600GT 256 ($120)

Basic gaming with medium quality settings up to 1680x1050, high quality at 1440x900 and below.

Mid-range Gamer ($520 Core Total):
Intel Core 2 Duo E6550 2.33GHz 4MB($180)
2GB DDR2-667 3-3-3 or DDR2-800 4-4-4 ($80)
GeForce 8800GTS 320 ($260)

The mid-range offering will allow games to fly at 1680x1050 and most high quality settings at 1920x1200.

Best Performance/Value Gamer ($740 Core Total):
Intel Core 2 Duo E6750 2.66GHz 4MB ($210)
4GB DDR2-667 3-3-3 orDDR2-800 4-4-4 ($180)
GeForce 8800GTS 640 ($350)

This setup will handle ultra-high detail settings at resolutions up to 1920x1200. If you want the max without breaking the bank, this is the way to go. If you need 2560x1600, start with an 8800GTX 768 card and seriously consider 2 8800GTS cards in SLI.