i know a lot of the material is up to individual professors; however, some of the progress in posting things online is hampered by the need to have the correct copyright acknowledgments on everything, etc. only a few lectures are actually recorded on video, and for most of those i think you need MIT web certificates. there's still a lot of good stuff that doesn't require certificates on many of the class websites, however.
another good resource is
http://mitworld.mit.edu/
basically a compilation of video lectures that have been given here, either on special occasions or the weekly colloquia, some good stuff there