This isn't Monopoly related but I won a free NES game from a Mountain Dew cap as a kid (well my Dad did).
I can't remember the year exactly but Pepsi had a promotion going where you could win one of three NES games - Super Mario Bros. 2, Dragon Warrior, or Tetris. The cap only told you that you won a game and Pepsi determined which game you would get. I got Dragon Warrior : (
It was free though so I didn't complain.