Films On Demand is an online collection of more than 15,500 full-length videos and more than 241,000 video clips, appropriate for academic research. Most videos are educational, documentary or archival films, and can be browsed by subject. Videos are streamed through the web, so they are available 24/7 and both on- and off-campus. Films On Demand also allows you to embed videos in Moodle and to create playlists of segments from different videos.
SchoolTube (like YouTube, but for schools)
TeacherTube (like YouTube, but for teachers)
Annenberg Media's Teacher Resources includes videoThis icon 
indicates free video.
EXPLO.TV
Webcasts, Video Clips, and Podcasts from the Exploratorium, "The Museum of Science, Art, and Human Perception"
Learning Zone Class Clips from the BBC
PBS Video. Lots of PBS material is free for viewing online. Browse programs or topics, or search.
SnagFilms.com
Professionally-produced films on a wide variety of topics
TED (Technology, Entertainment, Design): Ideas worth spreading
WatchKnow. Collects “all the best free educational videos made for children” and some for parents and teachers too.