a phenom ii x4 955 to 965 depending on compatibility and budget. get the black edition version for overclockability. add a good aftermarket cooler with the ph ii to keep it cool.
The Best AM3+ Gaming Processor is FX Processors lol... Get the Phenom II x4 955 BE so it can be OC. I Assume you already have a motherboard than get the Phenom II x4 955 BE but if you currently dont have the AM3 MoBo than get a cheap LGA 1155 MoBo and a I3-2125...