Depends on what else you need it for. Any fairly modern CPU won't bottleneck a 4670.
I have an Athlon II x2 (easily overclocked to 3.6ghz) and love it. It works great with my Radeon 5750, and it is a little less than $60 on Newegg for the 245. But if you spend $40 more, you could go for the quad-core Athlon II x4 640. Depends on how much of a power user you are.
EDIT: I don't know much about using ddr2 ram with it... You might need to get an am2+ motherboard and then the am2+ version of those cpus. But I really don't know much about that at all.
Mostly audio production (need a faster CPU than my current single core for rendering down files) and some gaming (not ultra high-end gaming, but I'd like to be able to play new games on medium gfx settings at least).
So far I think I'm gonna go with a quad core, but I wanna be sure I can use my ddr2 ram with a quad mobo. I'm pretty sure I can but would like to confirm with someone else.