I won't play anything fancy, mostly indie games and Valve games that I'll buy on steam. The only "demanding" game I have my eyes on is Bioshock Infinite, but it will use the Unreal Engine so I think that I won't be bottlenecked by the cpu/gpu since I don't play at 1900x1080.
I'm just going to re-use my PSU, GPU and HDD.
MOBO: ASUS P8B75-M LE
CPU: Intel Core i3 2100 a 3.1 GHz
GPU: GTX 550 ti
HDD: Seagate Barracuda ST31000524AS 1TB 7200 RPM 32MB Cache SATA 6.0Gb/s 3.5" (I got this for cheap before the flooding fiasco).
RAM: 8 GB Kingston @1333. (RAM is just cheap)
Case: CoolerMaster Elite 430 Black.
Exhaust Fan: Noctua's NF-S12B FLX. (I've heard a lot of good things about Noctua so I expect it to last me long enough to make it to my next build).
PSU: Thermaltake TR2 600w (I've been using this for 9 months with no problems with an OC Wolfdale Pentium dual core and a GTX 550 ti)
I'll most likely upgrade to a GTX 660 by next year, and also buy modular powersupply (Enermax or Corsair). Do you think I'll have any issues fitting the GTX 660 non-ti inside the 430?
While Willyroc's build is good, I would really advise against an AMD build, especially for gaming. That i3 will beat any AMD in gaming. Don't take my word for it, though. Look up the benchmarks yourself.
With the build you have suggested, the graphics card will be the bottleneck anyway, so you don't need to worry about the CPU (although maybe get an Ivy Bridge instead of a Sandy, unless you can find a sweet deal on a Sandy).
Also, I agree with Willyroc on the 7870 over the 660, as much of an Nvidia fanboy I am.