A favorite of many teachers. BiblioNasium is created for kids to "flex their reading muscles." Free accounts can be made for kids, parents, and teachers. Teachers can manage students by classes or groups, and parents can be notified of reading lists, reviews, etc. Students can easily discuss books and see eachother's reviews.
Write and read book reviews without having to log in. Search through book reviews by genre or by grade level.
3. Library Thing
Self-described as the world's largest book club. It meshes a library catalog with a social networking site where you can tag, rate, and review books.
4. Good Reads
Along with searching or browsing for books by title, author, ISBN, or by genre enjoy trivia, quizzes, and quotes from a variety of texts. Also, user generated lists allow you to search through "The Best for Book clubs," "Best Books of the 20th Century," and more.
Powered by Amazon. Search by tags, most popular, series, lists, and authors. The community provides insight into books and you can find members like you.
Figment allows you to share your own writing while also discovering new and emerging writers. Groups, forums, contents, and more.