LibraryThing is an online service to help people catalog their books easily. Because everyone catalogs together, you can also use LibraryThing to find people with similar libraries, get suggestions from people with your tastes and so forth.
How LibraryThing Works
LibraryThing is really two sites in one.
First, it is a powerful tool to catalog your personal library. Users add books to their catalog by entering titles, authors, or ISBN numbers. LibraryThing then searches the Library of Congress, all five national Amazon sites, and over 45 world libraries, and returns with precise book data. Users can then edit the books in their catalog, tag their books with their own subjects, and use the Library of Congress and Dewey Decimal systems to organize their collections.
LibraryThing is also an amazing social space, connecting people with similar libraries. It also makes book recommendations based on the collective intelligence of the other libraries.
Visiting this website is fun. They even have "unsuggestions" - telling people which books they wouldn't like to read based on their personal library! Click here to start your browsing.