Goodreads - See what your friends are reading.
GoodBooks.io - Largest curated collection of 8,500+ book recommendations.
LibraryThing - A home for your books.
Book Recommendations For Entrepreneurs - 1000+ books recommended by the world's top entrepreneurs
BookAuthority - BookAuthority collects the most recommended books on business, technology and science - as featured on CNN, Inc and Forbes
Oku - Track your book lists and get recs from your friends