i've actually always found it easier to understand the amd sockets. but anyway, for your athlon 2 quad core i'd say go with pretty much any mobo that has the 880g, 890gx, or 890fx chipset. the 890fx being the most expensive though. i have an asus m4a89gtd pro.
if that's out of your pirce range, then just get a mobo from a manufacturer that you like with an am3 scoket.