Through the blog of Atle Frenvik Sveen I was made aware of a service which may be said to be a crossbreed of IMDB and last.fm. Librarything enables you to register your books and even more interestingly get recommendations of books you might like.
I recently created a profile and I have just added the books resting on my desk. Adding book is easy as Librarything (potentially) searches more than six hundred databases in several languages. As I registered an account just a few days ago I do not have any experience with the recommendations. However, according to Atle they are quite good.
As you should see above, it is quite easy to integrate a list of your books into your web site using pre-made Java Scripts. Librarything provides an API as well but I have not tested it. However, it should be possible to integrate a whole lot of information about the books you have in your catalog into your site. The best thing is that the site provides cover scans for most of the books and they let you integrate these scans into your site as well, for non-commercial purposes that is. They did not have the cover for one of the books I had on my desk. However, they had the cover of an earlier edition of the book which was written by a Swedish author. EDIT: A user had uploaded that cover scan for this book as well so I was able to get a cover for this book as well.
I will start using Librarything, at least to see how it works. I might also include it here in my blog. Regardless of what I do, you should check out Librarything for yourself.