Albums that are primarily by one artist, that feature a "guest artist" for a track (or two)

No one's mentioned "My Curse" on Afghan Whigs' "Gentlemen?" Sung by Marcy Mays of Scrawl. There is also that song on New Order's "Get Ready" sung (at the beginning) by Billy Corgan.

More Clash, Allen Ginsberg on "Ghetto Defendant."