Creative Commons (search engine): http://search.creativecommons.org/
StockVault (free images): http://stockvault.net/
Find Icons (avatars and small images resource): http://findicons.com/
Morgue File (free images): http://www.morguefile.com/
Open Clipart Library (free clipart): http://openclipart.org/
You Tube: http://www.youtube.com/
Vimeo: https://vimeo.com/
Watch Know Learn: http://watchknowlearn.org/
Teacher Tube: http://www.teachertube.com/videos.php
Note: You are free to embed any video so long as it gives you the embed option. However, you must get permission to use any video that you are cutting, making changes to, or adding to a project.
Wikipedia (be careful as this is not considered to be a scholarly, reliable source; you must link back to any information you find on Wikipedia): http://www.wikipedia.org/
Curriki: http://www.curriki.org/
Collaborize Classroom Library: http://library.collaborizeclassroom.com/
*I retrieved much of the info found in this section from The Edublogger found online at http://theedublogger.com/2012/02/09/the-educators-guide-to-copyright-fair-use-and-creative-commons/
Free online courses for teachers in grades K-12
10 Education Sector Explainer Videos
Short videos that, well, explain various topics
75 Digital Tools to Support Formative Assessment
An extensive list of tools and apps
Per the site, list includes tried & true sites as well as newer 2.0 sites