In addition to Free Play Music, here is another site you might try for use with multimedia projects.
kitZu is a a collection of free, educational, copyright-friendly media resources. Students and teachers around the world can access pre-made collections, or "kits," of various digital assets - still images, background music, narratives, video and text.

Possible sources for royalty free music content (check for creative commons license)'s+Copyright+Free+Multimedia+Links