Anthony Kiedis (my fav by far).
Honorable Mention:
Jim Ward - At the Drive-In/Sparta
Chuck Robertson - Mad Caddies
Bjork
Gavin Rossdale - Bush (Not a big fan of the band...but always dug his voice).
Billy Idol
Chuck D - Public Enemy
Isaac Brock - Modest Mouse
Brody Armstrong - The Distillers
David Draiman - Disturbed