Actor Bill Paxton, star of Twister (the hero guy), Aliens (the scared guy), Stripes (the stupid guy), and True Lies (the slimy guy), as well as the star and director of one of the greatest videos ever made, Fish Heads by Barnes and Barnes, is another celebrity with three nipples.
From an interview with David Bradley (see link in Title):
He breaks into several refrains of whooping, "yeah-ing" and "right on, man-ning", and then, when pressed to tell me something that no one's ever heard about the great, the extremely famous cult icon Bill Paxton, he thinks carefully and volunteers, "I've got three nipples. Three. No one knows about that, but no one's ever asked me before. I guess it's about time I got it off my chest."
Nice one about getting it off your chest.