From Wikipedia:

The Wilhelm scream is a stock sound effect first used in 1951 for the film Distant Drums. Actor-singer Sheb Wooley is considered to be the most likely voice actor for the scream, having appeared on a memo as a voice extra for the film.

The Wilhelm scream has been featured in many films and television programs since. Alongside a certain recording of the cry of the Red-tailed Hawk, the "Universal telephone ring", the Goofy holler, the Tarzan yell and "Castle thunder", it is probably one of the best-known cinematic sound cliches.

A compilation: