Shona Whyte: this is going to be excellent for preparing teaching materials and presentations. Everything is CC, and there seems to be enough (recent) content to make it a good place to start.
Robin Good: Let's CC is a specialized search engine that can find any image, sounds, video or text that has been published under a Creative Commons license and is available for re-use.
Free to use.
Very useful. 8/10
Try it out now: http://eng.letscc.net/ ;
Via Robin Good, Dennis T OConnor, Lyudmila Anikina