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.
Bookicious - Find the best new book to read with books collections for makers, founders and entrepreneurs.
aNobii - aNobii is a social network for listing books, sharing insights, and meeting people.
Bookcelerator - A curated directory of books that will make you smarter
Riffle - Just good books and the readers who love them.