Creative Commons
From VideoLAN Wiki
The creative commons is an organisation which promotes making files avaliable for others to share, work with and build upon, normally for free. The creative commons publishes a group of licenses which allow a range of restrictions to be placed on the files, such as requiring that you give credit to the author of the file, or requiring that it is used as not-for-profit.
Websites
The following sites host at least some Creative Commons and Public Domain files:
