Use PCPartPicker to pick your parts.

I would recommend a build like this: http://pcpartpicker.com/p/bvPE

That Raidmax case isn't worth it when you can get a Source 210, that has much nicer features for building.

OCZ PSU is sold out, I'd recommend Antec's budget modular PSU instead of it or go with a OCZ 500W ModXStream PSU.

The Phenom is similar to the i3 2120 but both will perform similarly in gaming, if you want quad-core with Intel then go with the i5-2400 or i5-2500. If you're willing to spend a grand (i5 3570K, CM 212+ Cooler, Z77 Motherboard) then my suggestion will change quite a bit.

If you can get the 6870 it's one of the best $/performance cards out there right now.

Onboard sound is fine for the majority of users, if they need a subwoofer and rear out they can get a more expensive motherboard with those outputs.