In response to the OP:
Personally, I upgraded from a GeForce 9800GTX+ to a GeForce GTX 660. If you're apt to stick with NVIDIA, I would say this is a good option. Personally, I prefer NVIDIA's drivers and features, especially when it comes to graphics mods or PhysX support.
(I suppose that's an odd thing to say after my V-Sync rant above.)
It's about $80+ less than the 660Ti, but for some odd reason, it generally performs about the same. So it's a better price/performance ratio. At least as far as NVIDIA is concerned.
Otherwise, if you're not sure either way, run straight toward AMD like a dog toward bacon......Or a man towards bacon.......or anything towards bacon...........
Just treat AMD like it's bacon.
Not only will you get a great range of options, you'll also get a great price/performance ratio. Your General Purpose GPU processing will also be absolutely top-notch compared to NVIDIA, if you do Folding@home, Bitmining, Mathematica, MATLAB, etc.