This is a great primer for anyone unfamiliar with John Cage, his works, his humor and his ideas. This documentary was produced in the mid eighties as part of the PBS/American Masters series. It features interviews with Calvin Tomkins (Rauschenberg and Duchamp biographer), Merce Cunningham, Yoko Ono, Bob Rauschenberg, David Tudor, Leo Castelli, and many more.
Watch these, you won't be disappointed. Very beautiful and inspirational stuff.