LibraryThing is a wonderful online resource that allows users to catalog and create a virtual library of your own collections. It also includes features such as "to read" and "currently reading" collections, which is a great way to keep track of the books you have read/want to read . You can recommend books, review books and connect with other readers through the LibraryThing online community.
Up to this point, I had been using the service http://www.bookmovement.com/ to keep track of the books I have read and want to read over the past year; however, the site is more bookclub oriented and doesn't quite have the organizational features that http://www.bookthing.com/ provides, so I am switching over. The service is free - all you have to do is sign up for an account, so give it go and let me know what you think.
My profile can be found here - though it is so new that I only have a few books cataloged. If you create an account and would like to share your library with others, simply email me the link and I will post it for all to enjoy.