Goodreads - See what your friends are reading.
Bookstash - Bookstash is a free library of curated summaries from top nonfiction books.
LibraryThing - A home for your books.
Instaread - Read or hear key takeaways of any book in minutes
BookAuthority - BookAuthority collects the most recommended books on business, technology and science - as featured on CNN, Inc and Forbes
Book Video Club - Quick video summaries of the top business books for startups