John Wetton definitely; that break in the middle of "Lark's Tongues In Aspic, Part 2" slays me every time I hear it.
No one's mentioned Paul McCartney on "Think For Yourself"?
Holy crap, 93 posts before anyone mentioned Mick Karn?!?!?!?
His tone is so unmistakeably him and no one else, they had to make him the free Gimme Round in the new "I Can Name That Bass Player In One Note" reality TV show.