Off the top of my head (and googling to get the spelling right
Gunnar Nelson is a Goju-ryu black belt.
Bas Rutten, 2nd Dan in Kyokushin Karate.
Chuck Liddell is a Koei-Kan black nelt and nation champ in the sport.
Seth Petruzelli is a Shito-Ryu Karate 3rd degree black belt.
Frank Mir is a BB in Kempo Karate
Vitor Belfort trained under a student of Yoshizo Machida (can't remember the name) in Shotokan before his fight and victory over Rich Franklin.
Bigfoot Silva holds a black belt in Shotokan Karate.