*While these sites are "copyright friendly" be sure to check over the Terms of Use, pertaining to attribution.*
New York Public Library Digital Collection
While many of these sites allow you to use and even create your own music and sounds, be sure to always check the Terms of Use.
Aviary Music Creator allows you to make your own music
Copyright Friendly Music and Sound
dig.ccmixter helps you find music protected under Creative Commons so you already have permission to use items for videos, projects, podcasts, etc.
Soungle is a free online database to help you find all sounds and musical instruments samples on a mega online library. Simply search, preview, download, and it is all free
Myths about Downloading Internet Music from Messiah College
Copyright for Music Librarians
This guide is from the Music Library Association and can help anyone with questions or concerns about music copyright.