Goodreads - See what your friends are reading.
Readernaut - We are a small community of readers, sharing our adventures and supporting each other as we persue a life of learning.
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.
LibraryThing - A home for your books.
BooksLoom - There are more than half a million books published each year in the US alone.