GoodBooks.io - Largest curated collection of 8,500+ book recommendations.
Literal - Track your reading and discover your next favourite book
Goodreads - See what your friends are reading.
Readup - Track and improve your online reading habits.
Read This Twice - Verified book recommendations from people we look up to
Reading List - Reading List is a read-it-later app by Microsoft, which is bundled in Windows 8.1 onwards.