I use Discogs.com as a database to keep track of my collection. What's really good about Discogs is that it's also a marketplace where you can have wish list and easily buy the stuff you want, as long as there is a seller who has it.
Last night I got an offer on this item:
It's the first demo tape from Amon Amarth. The offer I got was quite big, $180. I'm not really a collector of Amon Amarth it's just a cool item that I got when I bought a small collection of demo tapes some years ago. Selling it would would give me money to buy more vinyls so maybe I will?