Book Jetty allows you to catalog, rate and review books, check availability through libraries (from 11 different countries), discuss books with firends, display on your blog
Librarything allows you to catalogue your books, using amazon searches, the Libary of Congress or other world libaries. Review, and rate these, and share with friends. Import from anywhere. Tag, list by book cover or lists, there are large discussion groups also, an early reviewers club, and LibraryThing widgets to share your book collection in various ways on your blog. Free accounts allow for 200 books. Over this, a small subscription yearly or a lifetime membership is available.