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National Geographic has some great one. [[http://www.nationalgeographic.com/|www.nationalgeographic.com/]]
Also you can check out [[http://www.hulu.com/|www.hulu.com]] it has a number of television shows and movies available.  The history channel also has some great videos to use. http://www.history.com/media.do (of course the opening ad for that drug that is commonly sent in spam messages doesn't bode well)