I recently discovered the site LibraryThing, which lets you catalog your books online and see how your collection matches with other people's. The social networking part of the experience is particularly nice. Right now, I'm busily engaged in entering all my books. I've been wanting to catalog them for a long time now, but I haven't had the energy. One nice feature is that you can type in the ISBN, and it will look up all the relevant information for you. It's a big time saver, although it's not always perfect. For example, there is a field for "Original Language" for the case of translations, but this is almost always blank.