Hmm....good question. It could be Snatcher for my Sega CD, Tengen Tetris for my NES, the Japan-only Star Wars Famicom game, Silent Hill for the Japanese GBA, Perfect Dark for the import N64, or Castlevania: S.O.T.N. for import Saturn. Now that I think about it, my God of War 2 E3 demo(taken straight out of the E3 PS2's used) would definitely be the rarest. Too bad it's not a full game.