Search for works licensed under Creative Commons, across media. Make sure that you follow links within results to verify works are licensed under CC. When in doubt, contact the creator directly.
Directory of additional Creative Commons content sources.
Resources for remixing, adapting, and sharing creative work - from the Boston Radical Reference Collective
This overview explains why and how you can find images to use in course & personal projects.
Want to use these images in a presentation, on a blog, or sharing on Tumblr, Twitter, or other social media?
Here are some sites where you can download sound & music files.