Goodreads - See what your friends are reading.
Four Hour Book Club - 300+ Books recommended on the Tim Ferriss Show 📚
Wisebooks - Free database of books recommended by world-class people
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
Good Books - Largest curated collection of 6,500+ book recommendations.