With your budget the GTX 560 Ti or the AMD/ATI HD 6950. Or wait a little while and get the new 7870's for around the same price as 6950. Or just wait untill the prices in the 6xxx series drop. This is just food for thought
Yea, first I was waiting for the 4xx series to drop in price, and now I'm waiting for the 5xx series to drop in price. If I keep doing this I will be waiting forever, so I'm probably going to go with the GTX 560 Ti. I've got the money for it and I'm tired of waiting.