I have been exploring youtube after reading an article from The New York Times about youtube and culture and started exploring for myself. I came across and astonishing number of videos of interest to me in a short search. In dance I was able to watch short clips of Nureyev, Alvin Ailey's company and others. I watched short clips of Glen Gould playing Bach and talking about Bach. These could be very interesting to show in arts classes. Here's an example.
It is easy to include the video in a blog, so you don't have to send students to youtube.