Photos Music Video
Finding Creative Commons and Public Domain Music
YouTube Music Library
Download copyright-free and sound effects directly from Youtube onto your computer. (https://www.youtube.com/audiolibrary/music)
Jamendo
Music from aspiring musicians. Thousands of pieces available--download full albums or individual songs. Some of the music here is free while other pieces are available for a small fee. On the free downloads, you have the option of submitting a small donation to support the artist. Many different styles and genres of music here. (http://www.jamendo.com/en/)
Free Music Archive
The Free Music Archive is an interactive library of high-quality, legal audio downloads. The Free Music Archive is directed by WFMU, the most renowned freeform radio station in America. Radio has always offered the public free access to new music. The Free Music Archive is a continuation of that purpose, designed for the age of the internet.
(http://freemusicarchive.org/static) Note: Free Music Archive has been purchased by Tribe of Noise and is undergoing changes in Sept. 2019. You can read more about it here: https://pro.tribeofnoise.com/fma.
CC Mixter
ccMixter is 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. Great site for finding background music for podcasts and videos. (http://www.ccmixter.org/)
Internet Archive
The Internet Archive has a huge collection of public domain music as well as other audio files available for listening and download. This can be cumbersome to search, but you might find just what you are needing. (http://archive.org/details/opensource_audio)
Library of Congress, American Memory Music collections
The Library of Congress has 51 collections of old music as well as a large number of other collections (photographs, advertisements, video, posters, and more) and makes them available for educational and research purposes. Check the copyright page for each individual collection for specific details on use restrictions. (https://www.loc.gov/collections/)
Incompetech: Royalty-free music
Download royalty-free mp3 files of music in many different genres. (http://incompetech.com/music/royalty-free/)
World's Largest Natural Sound Archive
Not really music, but you can find the sounds of 9,000 species here, documented in 150,000 audio files. (https://macaulaylibrary.org)
George Blood Music Collection
Through the Great 78 Project, the Internet Archive has digitized 25,991 78rpm records (so far). This collection has been made available for use in research, teaching, and private study only, so double-check any copyright information on individual pieces. (https://archive.org/details/georgeblood)