Amiga vs. Atari 1985 - Ahhh... the Bouncing Ball Demo, Deluxe Paint + more.
The New Amiga 1987 - Amiga 2000 and the Amiga 500. Video Toaster, MIDI + more.
The Amiga 3000 1990 - Amiga 3000, Amiga 2500, inc. first release of Lightwave 3D
Computer Graphics 1984 - Great 3D technical demos from Sillicon Gfx. A record breaking fill-rate on an Apple IIe (watch it go! Oh the power). I'm certain shows like these helped inspire a generation to code their own demos and cracktros.
Modems & Bulletin Boards 1985 - More of a talk show, but a nice retrospective.
Moleman 2 Demoscene: The art of the algorithms.
Commodore 64 in 1988 - Unfortunatly not a launch video, but focuses on the C64