I would get tthe i5-2500k if interested in ocing if not the i3-2120 will work equally as well as the 2500 and is cheaper. With the money you save upgrade the card to a 560 ti or gtx 480, the 560 ti is better. The case is a very good one, I have never heard of the brand of that ram get g.skill, kingston, or corsair.
I had another build with the same components, but with an i3 2120 and a sapphire 7850 2gb. I wanted to do stuff other than just gaming, but gaming is my top priority atm. Would the 4 cores of the i5 2500 be worth it, or should I go back to the 2120?