search.creativecommons.org will query major search engines(Google, Yahoo!, and Flickr) for materials which uses Creative Commons licenses(CC). This tool will help you find photos, music, text, books, educational material, and more which is build upon utilizing Creative Commons or free to share. You have to option to search for works you can use for commercial purposes and also search for works you can modify, adapt, or build upon.
Searching for Creative Commons using Firefox
If you are a Firefox user, you can use the built in Creative Commons search tool to search for creative commons works. Firefox search box defaults to using Google, but you can change the search box to Creative Commons by clicking the black arrow in the search bar as shown in the below picture.