Erik Satie: Vexations, score and music (excerpt).
Terry Riley: In C (1964)
Original recording (instrumental ensemble)
Another version (chamber ensemble)
Musical score here.
Steve Reich: Come Out
Brian Eno: Music For Airports (Ambient 1)
Alvin Lucier: I am sitting in a room
(Optional) In Bb (YouTube crowdsourced video/music project)