An overview of Creative Commons and shared culture by creativecommons.org
A Shared Culture from Creative Commons on Vimeo.
Lawrence Lessig, copyright activist, lawyer, and founder of the Creative Commons discusses the need for a shared culture in this TED Talk.
Creative Commons is a non-profit that offers an alternative to full copyright. With a Creative Commons license you can retain copyright on your work, but allow it to be used by others in the way that you specify.
General search engines for finding Creative Commons licensed work include Creative Commons Search and using Google Advance Search and clicking to search by usage rights.