I always find it interesting when I hear about celebrities or other well known people practicing jiu-jitsu. I stumbled across a jiu-jitsu wiki entry that listed the following famous bjj practitioners:
- Nicolas Cage (Actor): Trains under Royce Gracie. 
- Chris Conrad (Actor): Trains under Jean Jacques Machado. 
- Jim Carrey (Actor) 
- Steven Daniells-Silva (Dancer): Black belt under Andre Pederneiras at Nova Uniao. 
- Michael Clarke Duncan (Actor, Former Bodyguard): Holds at least a blue belt and trains at Gracie Academy in Torrence, CA.
- Michael Dudikoff (Actor): Has attended Gracie Camp. 
- Sean Patrick Flanery (Actor/Martial Arts Instructor): Brown belt. Studied for three years under Rickson Gracie at the Rickson Gracie Jiu Jitsu Academy in Los Angeles and studied at the Renzo Gracie Academy in the summer of 2003. He is currently the assistant instructor at Hollywood Brazilian Jiu Jitsu in Hollywood, CA. Past championships include 2003 Pan Ams, 2003 American Nationals, and 2002 1st Annual Inland Impire Championship. 
- Mel Gibson (Actor): Known to have studied with Rorion Gracie on the final fight scene for Lethal Weapon 3. 
- Olivier Gruner (Actor, Kickboxer)
- Steve Irwin (Deceased) (Wildlife Expert/Television Personality) 
- Kevin James (Actor) 
- Milla Jovovich (Actress/Model/Fashion Designer/Singer) 
- Chuck Norris (Martial Artist/Actor): Black belt under Jean Jacques Machado. 
- Richard Norton (Martial Artist/Actor/Stuntman): Black belt under Jean Jacques Machado. 
- Ed O’Neill (Actor): Black belt under Rorion Gracie Trains at the Gracie Academy in Torrence, CA  has been involved in BJJ since 1992 
- Joe Rogan (Comedian/Actor/Sports Commentator): Brown belt under Eddie Bravo and Jean Jacques Machado.
- Paul Walker (Actor/Model): Known to have trained under Ricardo “Franjinha” Miller. 
- Mario Van Peebles (Actor/Writer/Director) earned a blue belt from Ricardo “Rey” Diogo
- David Jason Silver (Actor/Wrestler)
- Ulises Bella (Musician): Trains at the Gracie Academy in Torrence, CA. 
- Harley Flanagan (Musician): Purple belt under Renzo Gracie.
- Rakaa Iriscience (Musician): Has been training since 1999. Trains under Ryron and Rener at the Gracie Academy in Torrance, CA. 
- Tommy Lee (Musician) 
- Herman Li (Musician) 
- Maynard James Keenan (Musician): Is a purple belt under Rickson Gracie. 
- Rikki Rockett (Musician): Brown belt under Renato Magno. Trains at Street Sports Jiu-Jitsu in Santa Monica, CA. 
- Pete Loncarevich (professional BMX racer from 1980—1994): 2nd degree black belt under Joe Moreira.
- David Mamet (Author/Film Director)
- John Milius (Writer/Film Director): Has been training in Brazilian Jiu-Jitsu since 1992 and co-designed the UFC octagon with Rorion Gracie with whom he is a close friend.  
- Guy Ritchie (Writer/Film Director) was a student of Roger Brooking at the Budokwai, where he also trained in Shotokan since he was 14. Guy Ritchie is now a purple belt under Renzo Gracie.
Who I would not want to roll with out of this list:
- Michael Clarke Duncan: This guy is a bus and he has a blue belt. I’d tap if he just took mount and laid there.
- Jim Carrey: He’s like Gumby. You can’t pull an armbar if he can already hyper extend it himself.
- Steve Irwin (RIP): This guy could hold the back of a crocodile. Enough said.
On another note, Sean Patrick Flanery did a good job in the movie Boondock Saints. If you haven’t seen it, you should check it out.