If you've watched the original movies recently, chances are you were watching the Special Editions — the versions with updated visual effects.
Lucky for us, Chris Gould of DVD Active has cataloged all of George Lucas's changes in visual and audio effects since the films' theatrical releases in 1977, 1980, and 1983.
Stars Wars: A New Hope

The Empire Strikes Back

The Special Edition release added a scream to Luke's previously silent fall after his duel with Darth Vader.
The later DVD release restored Luke back to his silent dignity.
Return of the Jedi
