In my humble opinion (and I have seriously contemplated this before), the best bassists in rock music are:
5. Bill Wyman of The Rolling Stones: he held the rhythm section down in what was probably the most rhythmical white band evar.
4. Cliff Burton of Metallica: he's already been said a few times, Anesthesia speaks for itself, although I'd put Orion with his best work.
3. John Paul Jones of Led Zeppelin: His bass lines were sometimes lost amongst his more active bandmates, but they show both proficiency and restraint, a rare combination in music.
2. Steve Harris of Iron Maiden: Iron Maiden is one of those special bands that thrives on its bass sound, even when most people focus on the guitars.
1. John Entwistle of The Who: If John Paul Jones was sometimes overlooked, John Entwistle was practically ignored as a musician in of the flash of the Townsend, Daltrey, and Moon. He was really a superior musician and was an amazing bassist.
I never thought my list of best bassists would come in handy. But lo and behold!
Edit: Entwistle's nickname was 'thunderfingers', must have been popular with the ladies.