Open Source Soundtracks

CCMixter

• Ccmixter.org hosts music freely shared by artists. The uploaded soundtracks are licensed under Creative Commons licenses, and most are Non Commercial.

Commercial

Hint: I'm not sure how to search for music by license, but if the author explicitly tagged it as 'commercial', you can find that here.

Non-Commercial

• Pling by Jaspertine - featured in source tractor video
• Alien Orange Lab by My Free Mickey

Others

• Jamendo - [1] - royalty-free access

• Type in Free Techno on Google - http://www.entropymusic.com/ and others
• RoyaltyFreeMusic.com - [2]
• MyMusicStream.com - [3]
• FreeLoops.com - [4]
• Guitar Improv from Lucas. Better than Madonna's Human Nature.

• DJBLUE - Mind Field -
  DJ BLUE / CC BY-NC 3.0
• Awesome soundtrack - what is it? - [5]