The Wilhelm Scream

In 1951, a sound designer on a Gary Cooper western called Distant Drums needed to overdub a scream onto a scene in which a man is killed by an alligator. He brought a contract actor into his studio and rolled tape as the man did six brief, anguished screams in one take. These screams were then added to the Warner Brothers sound library, and over the next couple of decades they found their way into dozens of Warner Brothers films.

Spielberg and Lucas seem to be particularly fond of the scream.

(HT: Boing Boing)