My only advice is, if you can get me to offer you $5,000 not to open the door, take the money and go home.

-- Monty Hall

Old story of Marilyn vos Savant's presentation of the Monty Hall Problem. Read to the bottom on the accidental ambiguity in the way vos Savant stated the problem; an interesting dimension that made Let's Make a Deal more than just the one probability problem. I love how Monty Hall himself knows the problem backwards and forewords, but mathematics profs still get tripped up. (Nothing against mathematics profs; it's a tough problem, and anyone who says it isn't is a jerk.)