Goodreads - See what your friends are reading.
LibraryThing - A home for your books.
Riffle - Just good books and the readers who love them.
Booqsi - Booqsi is a modern social platform built specifically for the book community, allowing you to engage with others in a more meaningful way about books.
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.