Music free to download and use for your projects
If you're interested in legal, free music downloads, for listening or to use as background for videos or other projects, here are three possible sources for you.
Musopen is a nonprofit organisation dedicated to making compositions that are in the public domain actually available. They produce recordings of classic music, which they then place in the public domain. You can also find sheet music at their website.
Jamendo is a platform for indie musicians. All music there can be downloaded for free and is available under a creative commons licence. Most seem to be limited to non-commercial use with derivative works distributed under the same conditions, but there is a section of their site where you can look for more open licences.
At Incompetech, Kevin MacLeod offers music, mostly "soundtrack" kind of things, under a creative commons Attribution licence, with an option to license pieces for a one-time fee if credit is not possible or not wanted.