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!
LibraryThing - A home for your books.
BookLikes - BookLikes is a free blog platform for book lovers. 100% independent and free.
aNobii - aNobii is a social network for listing books, sharing insights, and meeting people.
BookAuthority - BookAuthority collects the most recommended books on business, technology and science - as featured on CNN, Inc and Forbes