The Wilhelm Scream: "One sound effect that has found a following with many sound editors and observant movie fans is a distinctive scream named Wilhelm.
In 1951, the Warner Bros. film Distant Drums directed by Raoul Walsh starred Gary Cooper as Captain Quincy Wyatt, who leads a group of soldiers to stop some Seminole Indians from threatening settlers in early 19th Century Florida. During a scene in which the soldiers are wading through a swamp in the everglades, one of them is bitten and dragged underwater by an alligator.
As is usually the case with the making of a movie, the scream for that character was recorded later. Six short pained screams were recorded in a single take, which was slated 'man getting bit by an alligator, and he screams.' The fifth scream was used for the soldier - but the 4th, 5th, and 6th screams recorded in the session were also used earlier in the film when three Indians are shot, one after another, during a raid on a fort.
After Distand Drums, the recording was archived into the studio's sound effects library, and was re-used in many Warner Bros. productions."
[And many others from many studios. Thanks to the folks at Neatorama for reminding me of The Scream.]