Slashdot links to the fascinating history behind the Wilhelm, the most popular scream in film history:
“There is a very famous scream in Star Wars (Episode IV) that occurs when one of the stormtroopers falls into the Death Star chasm. No doubt all geeks are familiar with this scream, but may not know that it has been used in dozens of other movies and even has a name – “The Wilhelm”. There is a fascinating interview (transcript and audio) from NPRs “On The Media” that discusses the now cult-like following and history of this scream.”
Listen to the NPR interview, it’s spectacular.
DarrenBarefoot.com 
The Wilhelm Scream has at least two appearances in the Lord of the Rings trilogy, once from an Orc falling to his death from a ladder at Helm’s Deep in The Two Towers, and once from a Gondorian soldier falling from a Fell Beast during the retreat from Osgiliath in Return of the King