I am sure that many of you have either used, or heard of Shelfari. Shelfari is a social netoworking site for book lovers. You can search for books on the site by subject, series, author, etc. Currently my 6th grade class is compiling a list of "must reads" for other sixth grade students. They are extremely excited to share their book list on Shelfari. If you have checked out Shelfari and don't find it to your liking there are some alternatives.
22Books is a site similar to Shelfari in that you can create and share your own book lists. Your lists can be shared via link or embedding code. Users can also browse lists that have already been created.
Goodreads is similar to Shelfair and 22Books. You can create your own book list, explore video, author bios, and have discussions with other. Goodreads also has an option for taking pre-made quizzes. This might be useful to challenge the knowledge of the readers in your class.