"I, Lucifer" by Glen Duncan, is one of the funniest and most clever books I've read in a long time. Read it a few years ago. I think I'll put it on my reread list.

It is about a British writer who attempts suicide, and a deal is struck where Satan gets to occuppy his body and live as a mortal human, on a trial basis. God gives Satan a second chance, to see if he can behave himself while occupying a human body.

It either is now a movie or is about to be released. The movie will probably suck, as do most film adaptations of any book that had literary qualities.