I have a similar card (8800 GTS) and I'm waiting for AMD's 7 series. But if you have to buy now, you have only two options, the GTX 560 Ti 448 cores, or the 6950. 448 is a slightly better performer, 6950 is better bang for the buck and you can get more VRAM if you go with the 2GB version. Either choice is good. The regular 560 Ti is useless because it costs the same as the 6950 and is clearly the worse performer of the two.
The 448 is probably the best option right now if you want a single GPU solution and plan on sticking to that, but if you ever want to SLI it'll be hard to find another because it's a limited edition card.
Edited by GetTheMoney - 12/7/11 at 9:28pm