Well I haven't done this in a while. Not long recently put this together:
Operating System: Windows 7 x64 Home Premium
CPU : AMD A6-3670k 3.4ghz (4 cores 4 threads)
Ram: 4GB DDR3 Crucial Balistix Elite 1600mhz 8-8-8-23
Motherboard: Gigabyte GA-A55m DS2 FM1
Graphics: BenQ G2255 (1920x1080@60Hz) AMD Radeon HD 7850 1000/1314
Hard Drive: 2TB WDC Caviar Green
CPU Cooler: Arctic Freezer Pro 64 (old but still good these days)
Gaming case: CiT Vantage

Quite honestly, this AMD CPU for £70 paired with a good graphics card will play any game maxed out, even Battlefield 3.