Goodreads - See what your friends are reading.
inventaire.io - Keep an inventory of your books. Share it with others. Discover the books available in your network!
Readernaut - We are a small community of readers, sharing our adventures and supporting each other as we persue a life of learning.
aNobii - aNobii is a social network for listing books, sharing insights, and meeting people.
Riffle - Just good books and the readers who love them.
LibraryThing - A home for your books.