The Wilhelm Scream

I learned about this sound effect probably about 5 years ago or so. Basically, it's a scream that is used in just about EVERY movie that has an action sequence in it. I don't know if it's a Hollywood inside joke, or what, but now I hear it every time it's used in a new movie. You can read more about it here:

http://en.wikipedia.org/wiki/Wilhelm_scream