I'd go 7950 to future proof but it's up to you. The 7950 is better than the 660 Ti per a similar price point.
Check out my $1000 build here:http://www.squidoo.com/electronicandmore#module147312351
It's a pretty solid build per the fact that you also get an SSD as a boot drive (A 128gb Samsung 830 to be exact) and you get everything you need.
Or if you want to save a little and go with the 7870, which is more than capable especially if you overclock it. Check out my $850 build here:http://www.squidoo.com/electronicandmore#module147086871