Why use these images? From CommonKraft videos:

Copyright and Creative Commons

Images

Google Images Advanced Search - Go to Usage Rights section and click box "Only images labeled for reuse"
Flickr Creative Commons search A specialized search inside of Flickr that will allow you to search only for images that are using CC licenes.
loc.gov/pictures/ Library of Congress historical prints, photographs, political cartoons etc.
AnimalPhotos.info Thousands of free to use animals photos divided up in to easy to browse categories.
CarPictures.cc Thousands of Creative Commons licensed photos of cars, easily divided up by manufacturer.
Creativity103.com An archive of over a thousand abstract backgrounds you can use for free or just for inspiration.
OpenClipArt.org This archive of free-to-use clipart numbering around 11,000 pieces is filled with professional looking works.
PhotoEverywhere.co.uk A photo archive resource filled with travel and location photos from all around the world that are free for your use.
Photos8 Public domain photos
Wellcome Images Historical and contemporary images
US Government Photos and Multimedia Most materials is in the public domain, but read the disclaimers
public-domain-image.com/

Music and Sounds

www.soundzabound.com Free copyright friendly music
Free-Loops.com Free-Loops offers up thousands of sound effects, vocal loops, drum loops and a whole lot more.
ccMixter creative commons music
purple-planet.com Tracks are grouped into categories reflecting different moods.

Films and Film Clips

http://streaming.discoveryeducation.com
www.open-video.org
www.watchknow.org
www.youtube.com/edu
www.learner.org/resources/browse.html
www.clipta.com
http://dsc.discovery.com/videos
http://anyclip.com