I can't believe nobody's mentioned
Pino Palladino yet. He's one of my favourite players, and i can guarantee that everyone has heard at least one song where his snarling, melodic fretless bass can be heard. (Paul Young's "Every Time You Go Away" and "I'm Gonna Tear Your Playhouse Down" and Don Henley's "Sunset Grill", for example.)
Mick Karn is also a great fretless player (Japan, Rain Tree Crow).
And i like Jeff Ament's playing on Pearl Jam's "Ten".
Can you tell i like fretless?