For those of you that have heard of the Cheetamen games on the NES, you might know that Cheetamen II was never released, and never finished.
Somehow, a Brand New version of this game, still sealed, made it's way onto eBay. The Price is over $600 and still going.
Here it is: http://cgi.ebay.com/Cheetahmen-II-2-Nintendo-NES-Fact-Sealed-NEW-SUPER-RARE-/170680741978?_trksid=p4340.m1374&_trkparms=algo%3DPI.WATCH%26its%3DC%26itu%3DUCC%26otn%3D15%26ps%3D63%26clkid%3D2063698263164682879
( Glitchspot wouldn't let me link it. )