If te are an avid reader like me (I'm bookaholic) certainly you'll enjoy these places.
The Shelfari is the best place to mostra off my books, the favorites, the owned, the wish, the must read ones, etc. There are interesting groups and te can connect with people all around the world just like you. The shelfs can be displayed in your blogs, journals o sites.And it's all for free.

The biblioteca Thing is a very good site too, but for free te can catalog only 200 books. In the order hand, biblioteca Thing have a great BookSuggest searching that can recommend te a book from a book that te already read. It's very helpful.