If you're a book reader you're going to love this article. WorldCat.org has a searchable book/media catalog that spans over 1 billion items, from 18,000+ libraries worldwide (part of the OCLC cooperative).
From the home page you can search the catalog, by title, subject, person, etc. I did a search for Douglas Adams on of my favor authors, and I found his Hitchhikers Guide to the Galaxy books, DVD, audio, and more.
The main problem with any online library catalog (including WorldCat) is that the material you're looking for might not be available. All you're going to be able to see is the catalog entry for the item.