I discovered this fabulous web site last year, librarything.com. It is for anyone obsessed with books, and it makes my collection look teensy.
The details: it's a big thrill entering the titles you own or have read, and see all the covers laid out for you in different styles (okay, a nerdy thrill). They even sell a Cue Cat scanner that allows you to simply scan the barcode on the back and it's entered into your virtual bookshelf.
It gets better. Based on the books you own, and those you've rated and/or reviewed, the site supplies you with automatic recommendations of new titles you may enjoy. These are surprisingly spot-on in accuracy.
To top it off, it shows you other members who have similar tastes in books, and you can connect with them and discuss titles or any other book chatter that you wish. Really great site!
The site features an opportunity to review free books, and join groups that have similar interests.