Creative Commons Music and Sound Effects
"A true digital citizen understands how to ethically use the works of others to build his or her own creative products—music, art, video, stories, presentations--and share them with the world." -- Joyce Valenza
Online music, information, videos, and images have usage rights attached to them.
Creators attach different usage rights to their work. These rights include copyright (where works may not be reproduced without the publisher's permission) and Creative Commons (where works may be shared). Creative Commons licenses specify whether a work may be shared, and under which circumstances (for educational use, with attribution to the author, etc.).
The following links offer music and sound effects with Creative Commons licenses:
Youtube Audio Library
Community Audio from Internet Archive
Partners in Rhyme