The Wilhelm Scream. Cinephiles recognise it instantly (you only need to hear it once in the above video). It's been reused so many times since it was first recorded in 1951 that its inclusion today is almost beyond cliche, easter egg, or inside joke, and has become a combination of the three. (It's been in every Star Wars and Indiana Jones title thanks to sound engineer Ben Burtt, who resurrected its use.)
But did you know that it's been featured in at least 48 video games? From Ant City to Timesplitters 2, Mr. Juandrful at Kezins has gleaned the full list. It's longer than Wikipedia's list of games using the scream, and includes titles not yet released (where the scream is used in a trailer), so he seems to have done his homework. We had a little something on this back in 2006, but not a full list of games. So check it out. And booby prize goes to whomever comes up with the best onomatopoeic spelling of the scream, in the comments.
We've All Heard it: The Wilhelm Scream [kezins.com]