A great early-70's artist almost forgotten by all but the most ardent Pop fans is Emitt Rhodes, whose self-titled debut album is fantastic.
Everybody knows Crazy Horse as Neil Young's band, but they made a great album of their own in 1971, when guitarist Danny Whitten was still alive. Also on the album are Nils Lofgren and Jack Nitzsche (who did all Phil Spector's orchestrations, as well as a lot of soundtrack work. His own St. Giles Cripplegate album from 1974 is semi-Classical, and very interesting. He is also on Neil's Harvest album, and produced this Crazy Horse debut. Other production work he did was Graham Parker's Squeezing Out Sparks album, and three for Willy DeVille, a great singer), as well as Ry Cooder on a few tracks. Great album.
Martin Mull is now known more as an actor (he was on the original Rosanne TV show), but he made some great albums in the 70's. His turf was similar to another interesting songwriter, Dan Hicks---ironic humor. I find both much more clever than the better known Frank Zappa.