Is your book collection getting out of control? I certainly have the occasional fantasy of organizing and databasing up my books, and do keep them in a roughly thematic ordering. If you want to get really obsessive, though, this site will help you determine the first three Dewey decimal digits of your books, which I would think would be plenty for any home library. It’s also fun to browse aroundthis really impressive classification structure for all of human knowledge. And it is pleasing to see computer science linked with information and general reference, rather than with technology, though it is a little surprising that it doesn’t share a top level category with mathematics and other sciences.