Although I never used one, I was looking into a video card in that price range recently and concluded the ATI 4870 or 4890 was the best value. However, I did see the GTX260 on sale for a similar price and was considering that as well since I am an Nvidia fan.

The problem I had was actually finding one of these cards. Most of the stores around me only have GTS250's and HD5770's which cost more and offer only slight improvements (mostly directx support etc). I'd actually grab a 9800GT or 9800GTX if I could find one.