GoodBooks.io - Largest curated collection of 8,500+ book recommendations.
Tellico - Tellico is a KDE application for organizing your collections.
Goodreads - See what your friends are reading.
Book Catalogue - This is a simple book catalogue application, to store a list of your books.
Read This Twice - Verified book recommendations from people we look up to
Delicious Library - Delicious Library 3: Catalog your books, movies, music, software, toys, tools, electronics, & video games. Archive your life.