who can beat kimbo???????????

...Skilled fighters...

It seems people are either polarised into thinking Kimbo is a piece of shit or he's the greatest fucking fighter that ever lived.
My view: He's a very talented natural fighter, great chin, power, movement. He's got an excellent trainer in Bas Rutten who seems to have successfully overseen the transition from street fights to MMA.
People claim he has no ground game but Bas has been extensively training BJJ with Kimbo, he hasn't needed to use his ground skills because his stand up has been vastly superior to the two guys he's fought so far.

In answer to your question:
Definitely:
Fedor
Couture
Minotauro

Most likely:
Frank Mir
Crocop
Brock Lesnar
Fabricio Werdum

I genuinely think he could take Sylvia. Arlovski would be a great fight too.

yea, they're pretty much using his popularity to sell tickets and draw viewers.

Anyone who is in good physical shape and knows how to fight and is in his weight class or higher.

^Nah, Bas seems to be a good trainer, and Kimbo seems to be learning well, and also seems to be a tough mofo. I predict he will do well in mma, maybe well enough to get a chance to fight a real top level fighter. Maybe. Though I really doubt he'd stand much of a chance against any top 10 heavyweights if he makes it that far, and the top lhw like rampage could probably clean his clock.