Give books and receive books in exchange. Cost of the service is cost of postage.
Rich collections of audios (interviews, plays, lectures).
Fun way to create word clouds. Could be used in language as well as for creating holiday cards.
Book reviews for teens. Interactive blogs.
10 social networking websites about books reviewed
BookSprouts is a website where you can join and create book clubs. Members can vote on which book to read next, have book discussions in forums, post book reviews, and hold meetings.

Blippr is a website where you can add short reviews of 160 characters or less of books, movies, music, games, and applications. You can connect your account to many other social networks such as Twitter and Facebook where you can continue your conversations.