Chris Squire - Yes - One of the Godfathers of Prog, and had the most astounding tone ever.
Mike Rutherford - Genesis - Another of the founders of my favorite music, a great bassist and musician in general, and come on! Who doesn't think that his double neck Ric Bass prototype is awesome?
Roger Waters - Pink Floyd - Never flashy, but always just right for the song. His basslines lay down grooves that fit perfectly in each situation. The guy also writes some killer lyrics (Dark Side of the Moon and Animals for instance)
John Entwistle - The Who - What more can you say? Pioneered the bass-as-a-lead-instrument concept with Chris Squire and Mike Rutherford. Perfect for every song, and had a style that can't be imitated.
Greg Lake - King Crimson/Emerson, Lake, & Palmer - The guy was one of the first singing bassists in any rock band, can play tons of instruments, can play the crap out of a bass, and also writes pretty good lyrics (Lucky Man, anyone?)
***Honorable Mentions***
John Paul Jones - Led Zeppelin
Paul McCartney - The Beatles/The Wings
Chris Wolstenholme - Muse
just by the way....WHY DO THE BRITS AND CANADIANS GET ALL THE GOOD BANDS????