Goodreads - See what your friends are reading.
Bookcelerator - A curated directory of books that will make you smarter
LibraryThing - A home for your books.
BookAuthority - BookAuthority collects the most recommended books on business, technology and science - as featured on CNN, Inc and Forbes
Highly Reco - Book recommendations by awesome people
GoodBooks.io - Largest curated collection of 8,500+ book recommendations.