GeForce FX line should have something in that price range.
I recently picked up a PNY Verto Geforce FX 6600GT AGP for about $250. Absolutely wondeful card. I play WoW at 1600x1200 with all video options maxed...I average 50-60 fps during normal gameplay...grinding, PvP, etc.
Also running an SB Audigy 2ZS which is also an outstanding unit.
ATI is decent but second-rate in hardware quality and drivers. Many fanboys swear by them....but Nvidia is better.
HL2 is almost TOO fast with the new video card, but I'm getting used to it.
Good luck....holla if you need advice. Web design, SEO, computers, and networking is what I do.