BookDB is a free book catalog/catalogue program from Spacejock Software.
With BookDB you can enter all your books with author, category, publisher etc and print them out in a variety of formats.
If you're always going to book sales and buying bargains only to get home and find you've doubled up, take a printout with you! BookDB has a super-condensed print mode so you'll need a magnifying glass, but at least it'll save a tree or two. More Info »
BookDB also has lending library features. With them, you can add borrowers, loan out books, add multiple copies and so on.
You can use any barcode scanner with BookDB provided it sends the data as keypresses.