edit-(Sorry dudes, but looks like half the offered videos are no longer available. I guess it's just another web site looking to make money from banner advertising. guess I should have checked it out a bit more before posting a link to it here)
Watch Documentaries Online! Space Science, Astronomy, Physics Movies, Videos and more. Top Documentary Films. Easy Online Streaming. Free your mind!
http://www.streaming-madness.net/top-documentary-films/
(found this link lurking on The Mysteries Of The Universe discussion board: http://disc.yourwebapps.com/Indices/159729.html
Only checked out a few links, but it looks kosher enough. Norton says it's ok)