The Radio Broadcast That Panicked America on Halloween, 1938

On October 30, 1938, Orson Welles and the Mercury Theatre performed a radio play based on an H.G. Wells story entitled "War of the Worlds". The national broadcast caused panic and mass hysteria as listeners began to believe Martians had landed in New Jersey and were taking over the world. Here are links to the original audio and related resources.
More: Spooky October Radio
More: The Top 10 Scariest Radio Moments of 2004