A free account on Goodreads allows you to connect with friends, rate your reads, make a list of what you'd like to read, and discuss the books you love.
The site requires a free account, lets you rate your books, and organize them by collections. You can write reviews of your books and see what other users are saying.
Similar to Goodreads and LibraryThing but, Shelfari displays books that you've read, are currently reading, or plan to read visually by showing the book cover on a wooden shelf--creating a display image.
Kindred Works is a simple recommendation service that allows you to search by title or author. It provides a list of a few titles based on what you search.
