Monopoly? Would be cool (if a little complicated to make), but no one would ever be able to finish a game.
Edit: just thought of another one... Upwords. Its a cool game I used to play as a kid, its the same premise as Scrabble, but without all that 'ooh, you put a Z on a double letter space!' etc etc. Its just a simplified version, but you can put a letter on top of another persons word and make a new word.