Goodreads is, simply, a place to catalogue and briefly rate the books you have read. It's very simple and easy to use, although advanced features are available for those who want to take the time.
Wordie advertises themselves as being "like Flickr, but without the photos". It's a pretty good description. Wordie allows you to find and catalog your favorite words in any kind of list you choose. For language geeks, it can be a pretty fun place to hang out.