LibraryThing

Create your own online library! LibraryThing is an online service to help people catalogue their books easily. You can access your catalogue from anywhere, edit your information, search and sort it, "tag" books with your own subjects, or use the Library of Congress and Dewey systems to organize your collection. A free account allows you to catalogue up to 200 books.

LibraryThing also connects people. You can check out other people's libraries, see who has the most similar library to yours, swap reading suggestions and so forth. LibraryThing also makes book recommendations based on the collective intelligence of the other libraries.