I mostly play less needy games like Dota 2 and Starcraft 2 but I also play some rpg and adventure games also liek Skyrim and Fallout games and would like everything to run looking pretty with a good fps. I will be playing on a 1080 screen.
Also if it matters I the CPU will either be a 8320 or a 6300 on a 990 board and I don't mind ocing if I needed to.
If it's just that, a GTX 650 Ti Boost 2 GB will do you just fine. If you want to play something more modern with Ultra settings or play Skyrim with more intensive mods, the GTX 760 will do a good job of that. That or a 270X if you want something slightly less powerful for $200.
And I'd go with an 8320, more cores = moar better. Then again, depending on the price and your needs, a 6300 will do fine.
I have to say in Starcraft 2 you won't see a big difference (if one at all) using the 6300 v 8320 because Starcraft only uses 2 cores anyway. But of course the other games may make use of those extra cores. So as st33med said 8320 could be better but 6300 will do you fine.
If you can find a GTX 660 on sale buy it, it will eat most games for breakfast at 1080p other than that go for the GTX 650 TI boost.