recommend to you a BFG or suitably equivalent 8800 GTS 320mb overclocked by factory. BestBuy had this a while back on sale for 279.99. The best satisfaction per dollar by far.
BFG - GeForce 8800 GTS OC Graphics Card - BFGR88320GTSOCE
rebates gone though
currently, newegg had the XFX 8600 overclock 256mb for 119.99 after 20$ mail in rebate. not nearly as fast as the 8800s, but it will run many current games maxed and also has DX10 support.
Newegg.com - XFX PVT84JUDD3 GeForce 8600GT 256MB 128-bit GDDR3 PCI Express x16 SLI Supported Video Card - Retail
avoid ATi