I recently came across two resources for teachers that utilize the Creative Commons to provide photos and videos you can use in your lessons and presentations.
Compfight - http://compfight.com/ - Compfight is a Flickr Search engine that will allow your searches to display creative commons and commercial license photo that other users have uploaded.
Videezy - http://www.videezy.com/ - Videezy provides B-Roll HD video that other users have uploaded. You do have to create a free account to save and download.
In my first sentence note I said resources for teachers. I have not been through every photo and every video to determine questionable material (and what one calls questionable others may not). As always teachers should thoroughly preview any sites they intend to use with students.