Mike Tyson signed with Pride to do boxing exhibitions only. As of right now, he's not going to do any kind of real boxing/fighting. And Bob Sapp is still technically under contract with K-1 even though he walked out of the last event he was scheduled for.
Hateraid, I'm a big Cheick Kongo fan as well. Really, I'm a fan of any man who throws vicious knees like that from the clinch. Love it. I think he'll make noise in a weak UFC heavyweight division.