I wouldn't ever kill anyone for money. Not ever... I couldn't. I'd probably do a fair few things but I doubt I'd chop my dick off like the said above.... or do anything uncomfortable like eating shit or sucking dick other people have mentioned here.
There's plenty of other things I would do.
Though I do have a friend who said he'd suck 50 dicks and take it in the ass for a million dollars. I asked him why and he said that with a million dollars he could change his whole life and the past wouldn't matter. He has money to do whatever he wants. I could only imagine what he'd do for a billion dollars.