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

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