Rights-free Media Sources
Numerous sites exist that allow full or partial use of audio & visual material. The usage rights vary widely. Creative Commons (http://creativecommons.org) is an organization that has codified the release of rights to varying degrees in publicly available media. Many private services have adopted these standards and use them within their services.
Be sure to check the specific use cases you intend with any sourced media—above all pay particular regard to referencing the original work as requested: it is simply the best behavior.
Music & Audio:
Free Services
SoundCloud Creative Commons:
http://soundcloud.com/creativecommons
OpSound:
http://opsound.org/music/
Free Music Archive:
http://freemusicarchive.org/
CCMixter:
http://www.ccmixter.org/
Jamendo
http://www.jamendo.com/en/
8tracks Creative Commons
http://8tracks.com/mixes/creative_commons
Vimeo Music Store:
http://vimeo.com/musicstore
Open Music Archive
http://www.openmusicarchive.org/
Public Domain 4u
http://www.publicdomain4u.com/
AudioFarm
http://audiofarm.org/
SonnyBoo
http://sonnyboo.com/music/music.htm
Archive.org
http://www.archive.org/details/audio
Sound Click (you have to select from the pull down menu to get creative commons)
http://www.soundclick.com/business/license_list.cfm
MobyGratis (songs from Moby––not for profit: not sure where kickstarter falls––spirit, not letter)
http://www.mobygratis.com/gratis/list
Paid services
Friendly Music
http://www.friendlymusic.com/
You Licence
http://www.youlicense.com/
Magnatune
http://magnatune.com/
APM Music
http://www.apmmusic.com/
Audio Socket
http://audiosocket.com/
Pump Audio
http://pumpaudio.com/
Graphics:
The Noun Project
http://thenounproject.com/
Icons for everything. Note all require attribution.
Video & Still Images:
Video and still images:
flickr
http://flickr.com
flickr allows users to search for rights-free video and images in the advanced search settings by selecting “Creative Commons images only”.
Wikimedia Commons
http://www.wikimediacommons.org
Vimeo
http://vimeo.com
vimeo allows those who upload videos to designate them with Creative Commons licenses. It is not possible (yet) to search the site for designated videos only.
With each of the services, be sure to double check that the released rights match with your intent for use.