Have you seen this yet?
It's called LibraryThing, and it's an online cataloguing system for books. I signed up for an account, and so far I think it is AWESOME! It's SUPER easy to use, especially compared with the program I bought to do this. (Don't remember what it's called off hand, but I had to enter individual ISBNs for all my books - very time consuming, and I gave up on it after a while). I haven't entered many books yet, but I intend to keep adding books as I have time. And buy a membership, since it's DEAD cheap. My username there is herebedragons if you feel like checking out my shelf.
ETA: Forget what I said about how I was going to buy a membership. I just went and bought it. :D