Doug Ferguson, original bass player in Camel was pretty awesome, as was Andrew Latimer when he picked up a bass guitar as well.
ALso a big fan of Richard Sinclair who played bass mainly with canterbury rock group "Caravan" (it's dromedary day I suppose) and also did a stint as bass player with Camel in teh late 70's.
Also gotta mention Chris Squire (Yes) in the discussion.
While on the prog rock track, in more recent years, how about Colin Edwin of Porcupine Tree?