ROFL! We actually play this game at work all the time (not passing out millions for head, but the would you game)
We have come up with tons of stuff. What I have found from a pretty diverse group is that for roughly 1 million, people will do most normal stuff (head, eat a used tampon, eat crap etc etc)....but for 10 million they will do just about anything and for 1 billion, they will do anything you want.
One of the guys said he would ****, kill and burn his own mother for 1 billion dollars. One would eat a aborted *****.