Bicycle Blue Book is a new website with the aim of helping people navigate the world of used bikes. It is a guide to both buyers and sellers. Using a database made up from actual transactions over the past 7 years, they created a useful tool for everyone. In addition, there is also a market place to buy or sell used bikes.
While the site is far from comprehensive, it is the best attempt we have seen thus far. As the site develops and grows, and they obtain more data, it should only get better.
Check it out here
On the open market, an item is worth whatever you can sell it for, so value is something that will vary both regionally and seasonally. For the buyer, it is best to look at the end of the season; for the seller, the beginning.