A series of animated shorts titled "Geometry of Circles," featuring music composed by Philip Glass, kaleidoscopically tranced out legions of Sesame Street viewers in the early 80's.
The clip above features four of these shorts strung together almost seamlessly, even though they were first broadcast separately, in some cases years apart. According to the Muppet Wiki, "Geometry of Circles" dates back to 1979.




This is, of course, not the Muppets' only link with experimental and avant-garde music; Jim Henson also voiced a pioneering early film, "Limbo: The Organized Mind," by one of the godfathers of electronic music, Raymond Scott (as heard on the Manhattan Research, Inc. box set).
Here's a 1974 live version (!!) of ""Limbo" from The Tonight Show. Also cf., Henson's short film "Ripples," with music by Scott.