shelfari, your personal, online library
Shelfari just recently joined my bookmarks bar (i.e., about 20 minutes ago when I stumbled across it via the WordPress plugins codex), but after spending those 20 minutes rapidly adding books and reading others' comments about them, I'm in total love.
You create a free account (free is always better), create your personalized URL (similar to flickr) and then go to your shelf and start adding books. Fortunately you can add via author or title.. if you do author, it'll give you a list of all their books (perfect for me, since when I find an author I like, I tend to buy all their books). And each book has their own page on the site where you can go to chat about the book with other shelfari users.
The top two reasons I love this site? The interface is beautiful (actual shelf, with your books on them AND you can click-and-drag them to whatever order you wish) and I can add widgets to my blogs to show what I have or what I'm reading. I have hundreds of books, and while I've always wanted to catalogue them, the task was just far too daunting. This site allows me to catalogue everything I have at a much quicker pace.

