AT&T's official YouTube page includes an incredible number of educational videos from their archive including work by Jim Henson and Saul Bass.
The Viewtron System and Sceptre Videotex Terminal (1983)
The Hello Machine
Microelectronics Video Disc Exhibit
Music in Motion
Crystal Clear
Lightwave
Bottle of Magic
The UNIX Operating System
Telezonia
Now You Can Dial
Principles of the Optical Maser
Genesis of the Transistor