The i3 2100 is a great buy (2120 can be had for the same price, look around). I run an i3 2120 in my gaming rig with a 6870, and it is a total beast for SWTOR, around 100 FPS with everything maxed at 1080p.
That said, I wouldn't buy a dual core CPU right now, even though I admit the i3 is still a VERY strong CPU for all of today's games. I think in the next year the quad core and above will really start showing their worth over dual cores. Of your choices I'd go with the i7, though I really think you should consider an i5 instead, the i7 is not better for gaming than the i5 by any appreciable amount.