Reverend Rock
cool music and hot coffee
I would agree with this (of course I'm very biased on the subject - being a bass player and playing in a Zeppelin tribute band).
I wouldn't know how to go about making a case for it though...
Well, to begin with, we could point to what he did in addition to being a superb bassist (which he certainly was). He was also the band's keyboardist in the studio (and occasionally on stage as well), and his work on the piano, mellotron, and sythesizer has always been criminally overlooked (just listen to his work on "The Rain Song" from Houses of the Holy and consider how important the mellotron is to that piece).