I found a very cool website yesterday, cool that is if you're a geeky book person like me, called LibraryThing. It allows you to catalogue (or catalog if you're American) your book collection. I don't have many of my books here in San Jose but the few that I do have are now listed on LibraryThing, complete with pictures of their covers. The covers are a very satisfying thing, reminding me as they do of the treasures inside the books and the pleasures I've had reading them. I'm hooked. Here's the cover of the edition of Bleak House that I'm currently reading.
The site's not just a private database though, it has a social component. You can see what's in other people's libraries, chat, write book reviews, and you can get selections and recommendations based on the combinations of books in the various libraries, ie people who own Bleak House for example tend also to own books A, B, and C. It's very accurate, much more so than Amazon's "people who bought this, also bought that" recommendation tool.