Close Encounters of the Third Kind:
When the government researchers try to communicate with the "Internet" they play a series of notes on a keyboard. This is an homage to the scene in the 1977 movie, Close Encounters of the Third Kind. In the film, the humans try to communicate with the UFO using music played on a keyboard. (The original note sequence from the movie was G, A, F, F, C; in South Park they played the last note differently ostensibly to avoid copyright violation.