Any of the Gracie brothers would fight him for sure.
It's all they do, it's how they came to fame. I train with a Rickson Gracie taught instructor and met Mestre Rickson once. While I don't think Rickson would, I know all the other Gracie brothers and cousins and what not would fight him.
Many others out there I think could take Kimbo as well. Although I gotta say, I'd love to see Mike Tyson and Kimbo square off together.
This guy is a monster. Built like a tank and is awesome.
The third guy from the left and the guy at the very end on the right, I'd put ALL my money down that they'd take Kimbo out inside of three rounds, only cause they'd spend the first two playing with him.
I'd never think of going against kimbo, simply cause I train for self defence and ring fighting. Would I run from him, nope, but I don't train to fight like that. The guys I posted do.