That depends a whole lot on the motherboard and RAM. Do you already have a motherboard and RAM, or are you trying to configure a new build right now? If so, what's the budget for the build?
AM3 or AM3+?
For AM3 there is nothing you can get new, but here is a list of processors that fit the socket (I run the 965, the X6 1100T is great)
Motherboard and DDR2/DDR3 permitting.
Yeah, so I just considered those null and void, and there arent any on PCPartpicker (which reminds me I was going to post that link) http://pcpartpicker.com/parts/cpu/#k=3