Free & Creative Commons music
Musicians make their music available for use but remember to read the conditions of use. It's frustrating to put hard work into your production to find you can't share it as it violates copyright. Creative Commons licensing makes it so much easier these days but you still must acknowledge your the creator or source.
Free Play Music
Music available for student projects. Various level of licence apply. Categorised under style and feel for easy selection.
CCMixter
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. Samples, remixes, podcasts and recommendations.
Incompetech
Large variety of royalty free music organised by genre or feel. Check conditions for use in the Music FAQ. Keep in touch with this community via Kevin MacLeod's Incompetech blog.
Thefreesoundproject
A collaborative database of Creative Commons Licensed sound effects. All work must be attributed to the original author.
Free Music Archive
Great source of a variety of genres of music. Music is free with conditions for use that you will find on the track information.