I stayed up later than I should have last night, because right before I went to bed, I found about something called "The Wilhem Scream". It's a scream that was used in a western back in the early 50s, and then has been used in SEVERAL movies since.
After it was used in the original Western, the sound guy from Star Wars was looking for a scream sound effect, and found the scream....and since Star Wars, the scream has been added to several movies including, Batman 2, Toy Story, Reservoir Dogs, Indiana Jones, Spaceballs, Lord of the Rings, Anchorman, Sin City, Lethal Weapon 4 and more!
Here's a couple of videos showing you WHERE in some of those movies
The person, they believe voiced the "Wilhelm Scream", was Sheb Wooley....who is most known for the song "Purple People Eater".