Anyone know of any attempts to keep track of recent valuations of items?  There's a lot of "this has been going for a lot the past few months" and "these values have dropped a lot", but that's obviously based on individual experience.

What I've done has been to search Completed Listings on eBay and use an average of the last three auctions, but that's ad hoc at best.  I sometimes double check with NobleKnight or TitanGames as a sanity check as well, but their prices are generally inflated by at least 20% over what you can get on eBay (which isn't all that bad since they're actual storefronts).

The only item I plan on selling of even moderate interest is a Complete Book of Necromancers, and those go for about $10-25 I think depending on condition.  But I always like to have a general idea of how much something is worth before posting.

And another way to do it is to use the Price History in AuctionSieve - eBay auction search software tool | AuctionSieve