Well, the 680 for $340 is the best value, but of course it is used and you'll have to decide whether that is ok with you. Basically, at $350 you are stuck with the 7950. If you are open to SLI/XFire there are some additional options for around $350 such as 2 x 6870 or 2 x gtx 560.
I will also point out that while it isn't quite as powerful as a $350 card, this $210 GTX 480 is a pretty good price for its performance (that is, if you can take the heat!): http://www.newegg.com/Product/Product.aspx?Item=N82E16814130759
Edit: I guess Newegg thought the price was too good too, it's up to $220 that quickly.