sengoku 3 for the neo geo is the rarest game I own, only 500 were made to begin with and many copies were sacked (for all intents and purposes destroyed, judging by comments on neo-geo.com along with some evidence I unintentionally obtained I would be suprised if over 100 copies or more were sacked) bought just before its values started climbing (paid 130 for it, runs around 400 on ebay now)
I also have an odyssey rifle, which is really cool, and a miracle piano with the nes harness, I've been really enjoying the miracle piano
I've also got a bunch of really odd ball controllers for various systems ranging from how do you use this thing (a controller for the ness that layed out with the d-pad on one side and the action buttons on the other), to the totally awesome an snes controller made with real arcade parts
I've also got a bunch of games that are in demand as well as many more rares games, but I just listed my single rarest game along with some cool accessories