Poker is often used to launder money.

A few card rooms in LA have been busted for this recently, including the Bicycle Club.

Basically the launderers play a fake poker game against an accomplice heads up "opponent". The accomplice is the one who shows up with the dirty money (supplied by the launderer), and then the accomplice "loses" that money to the launderer, who then declares it as high stakes gambling winnings.