Every system has a Holy Grail usually based on rarity. The chapionship carts for Nintendo. The Half Life proto / loaner for the Dreamcast.

What I would like to know is what is your personal Holy Grail? What game would you like to own that you don't already? It can be based on rarity or just the fact that you really enjoy the game.

Mine would be Panzer Dragoon Saga for the Saturn. I had parts 1 and 2 a few years back and thought they were great games even though I didn't get to finish them.