I just listed three unique items on ebay: two of the more uncommon "Not For Resale" Nintendo DS promo kiosk demos and the Sega CD/Mega CD Pro CD-X cart which allows import games to play on any Model 1 console.
The DS demos are on eBay and the Pro CD-X cart is on chasethechuckwagon.com. Check them out.
DEMO Castlevania Dawn of Sorrow Nintendo DS cart:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=290252302557
DEMO Pokemon Trozei Nintendo DS cart:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=290252310403
Sega CD/Mega CD Datel Pro CD-X Import Game Converter cart:
http://www.chasethechuckwagon.com/it...tem=0000006903