Creative Common Music Sites

http://audionautix.com/

http://www.danosongs.com/

http://freemusicarchive.org/  (must check licenses here)

http://incompetech.com/

http://www.jimmyg.us/ (free sign up to download)

freesound.org (free sign up to download) (sound effects & ambient tracks)

With Credit Given (Creative Commons) - Free!

 By default, they are licensed under Creative Commons: By Attribution 3.0. To use this license, simply attribute the music in your piece (website, film, phone system, etc.) as is reasonable to the medium.

There is no cost to use music under the Creative Commons License.

Step 1: Give Credit

Short example:

Title Kevin MacLeod (incompetech.com)

If you'd like to include the full license for legal reasons, you can do the following:

Title Kevin MacLeod (incompetech.com) 
Licensed under Creative Commons: By Attribution 3.0
http://creativecommons.org/licenses/by/3.0/

It is important that you replace the word Title with the Actual Title of the piece that you are using!