Yahoo! Offers Public Domain Search Engine

The Yahoo! Search for Creative Commons website will help you find content on the Web - text, books, educational material, etc. - that has a Creative Commons license and is therefore is free to share or build upon. This search engine helps you quickly find those authors and the work they have marked as free to use with only "some rights reserved." If you respect the rights they have reserved then you can use the work without having to contact them and ask. In some cases, you may even find work in the public domain -- that is, free for any use with "no rights reserved."