Do you have a budget? Usually an i5 is considered good for gaming purposes. The newest haswell cpu's need a BIOS update before they can work on that B85 though, so if that is a problem you can consider an older i5.
Well there's the Pentium G3258, I've got one of these myself right now at 4.2ghz and for how cheap it is the little guy does alright. For $69.99 it can't be beat.