21 is a film about M.I.T. math whizzes who figure out a way to make a killing counting cards in Vegas. So in terms of a soundtrack, we're definitely going to need a busy tune for the scene in which they put their heads together and hatch that Plan So Crazy It Just Might Work. Check, thanks to LCD Soundsystem's appropriately titled "Big Ideas." Then we'll have to have something for a slow-motion strut through the casino. Lots of good options here, but our money's on Rihanna. Now, what's missing? Ah, yes. Something for when everything goes horribly, terribly wrong. Thank you, Unkle!