I'm getting ready to build a second budget gaming PC for my kids. First PC has Athlon II x3 450. I was able to successfully unlock the core on the one. I will be purchasing ASrock Extreme3 870 for the MOBO. Will be using HD6850 gpu and I'm not really interested in OC beyond what can be handled by stock. Kids mostly play WoW, but who know what they will play in the future.
I'm looking at either the x3 450 again, X4 955 or as a wild card the Phenom II X2 555. I think the safe budget bet would be x3 450. If I can't unlock the core I still have 3 cores. The X4 955 would be my preference, but that's stretching the budget. Now the wild card II x2 555. If it unlocks, that's great. If it doesn't unlock, well?
X3 would also be my choice on a budget. Particularly if it allows a little more money for a better GPU. I currently have a X3 445 (unlocked 4th core) and a AMD 6850, both budget parts but it manages to play anything I throw at it at decent settings.