The only QBs I would trade Carson Palmer for are Peyton Manning and Mike Vick. I'm not even sure that Vick would be a better QB for the Bengals... actually, it is doubtful. I still couldn't pass up that excitement.
Michael Vick is too much of an injury risk. He got hurt again yesterday. That's not the kind of QB you want in the NFL.
I would add Ben Roethlisberger to the Peyton Manning list though. It'd be hard to argue that Palmer is better than Big Ben.