Here's a possibly quite rare item that I've just seen pop up on eBay:
Sega Channel adaptor for Sega Genesis RARE
I picked up one of these at the local Flea Market back in October 2009, and I’ve been curious to find out what mine’s worth. It allowed users to use their cable TV to download video games on demand to their Sega Genesis back in 1994! That’s before the internet boom!
The one being sold above is missing the power adapter and the coaxial cable that they normally came with. Check out my old blog entry to see a picture of it with these accessories.