Free stock photographs

We keep getting asked for sources of photographs to be used in educational materials - Moodle, worksheets, etc. (The lazy option is of course to use Google Image search and sod the consequences).
Thus I'm putting together a package for my academic colleagues which will hopefully return them to the straight and narrow. So we might as well share them with you, dear reader.
All of the sites mentioned here offer varying collections of royalty-free, copyright-free, Creative Commons, public domain, etc. images. Generally, all that is required is an attribution which, after all, is common courtesy.
I'll have to admit that the site that I use most is Flickr and the easiest way to find Creative Commons photographs there is to use FlickrCC which is a Flickr CC search engine written by Peter Shanks. A very good place to start.
Anyway, these sites might just keep the Intellectual Property Police off your case:

• stock.xchng
• Open Stock Photography
• Geek Philosopher
• NASA Image eXchange (NIX)
• FreePixels
• Studio 25
• Image*After
• Everystockphoto (search engine)
• openphoto.net

And if that's not enough, Intute produced an tutorial, Internet for Image Searching. Send them back to class!

And lest we forget, the above image is Class Room by cobrasoft via stock.xchang used under licence.