FreeSound - A selection of sounds sorted by tag, mostly CC Attribution.
BBC Sound Effects - 16,016 BBC Sound Effects in wav format to download for use under the RemArc Licence. Can be used for personal, educational or research purposes.
CC Mixter - Provides sample packs, remixes, A Cappellas, and playlists with CC music.
Free Music Archive - Browse by curator or genre.
Proud Music Library - Sorted by music style and genre, also character, instrument, and tempo.
Public Domain Music - Sheet music, links to MIDIs, and Royalty Free Music.
AudionautiX - Sorted by genre, mood, and tempo, CC 3.0 Attribution.
Audio Jungle - Royalty free music for sale.
Icompetech - Music in the public domain from around the web
Cylinder Preservation and Digitization Project - Digitized wax cylinders, MP3s available (CC-BY-NC), WAV files - nominal charge.
Our Media - Multimedia archive hosted by the Internet Archive. Licenses vary.
Public Domain 4U - Songs in the public domain.
MUSOpen - Login required - classical music in the public domain.