Someone gave the guitar player in the band I play in a cd containing ~15 funk tunes that I hadn't heard before and after searching I found it. It's out on Rhino and is called "What It Is! Funky Soul And Rare Grooves"
It's a 91 song 4 cd box set of tracks taken from Warner Bros and Atlantic archives dating from 1967-1977. If your a fan of the funk and looking for some outstanding bass and horn lines it's not to be missed.