It just occurred to me as I was driving in to work today that the bass line to "Sympathy for the Devil" is, while not terribly complicated, one of the greatest bass lines; that song would really be totally pointless without it. Simple, insinuating, sensual, sloppy--amazing.
Another simple but ingenious bass line: "Once in a Lifetime" Talking Heads
What are some others? (And please, no bass solos--maybe in another thread)