Space Fantasy Zone (Prototype - Turbo Duo)
Angels II Holy Night (Graphic conceptions - prototype - Turbo Duo)
Silky Lip (REALLY small demo prototype - TurboDuo)
Atomoic Runner Chelnov (prototype - Saturn)
There *IS* actually a few originals of Space Fantasy Zone. There was one on Yahoo Japan Auctions about a year ago. It cleared $3,000 USD.
Some other goodies, but not that rare:
Phantays Star Collection (sealed - Saturn)
What's Shenmue (demo - sealed - Dreamcast)
I sold most of the rest of my stuff, lke a sealed Sapphire... needed the cash.