flickr/ creative commons is a great resource that has many different photos you can use in different presentations. It is the same as flickr except these photos all have a creative commons license.
ccMixter is a community music site featuring remixes licensed under Creative Commons where you can listen to, sample, mash-up, or interact with music in whatever way you want. This music could be used by teachers and students in different presentations that they create.
All the music on jamendo is available under one of the six Creative Commons licenses. They authorize free music download and enable the artists to promote their music while protecting their rights.
Wikimedia is a database with freely usable media files that anyone can contribute to. The text is available under the Creative Commons Attribution/Share-Alike License.
SpinXpress is used by independent global media producers to create videos, music compilations, and other collaborative media projects. Users can search for Creative Commons licensed content such as videos, images and music are available to the public for free legal sharing, reuse, and remixing.
This is a collection of constitution photos you could use when teaching the concepts of the United States Constitution.