I can't remember where I heard it, or what made me try it, but the only thing that worked for us was the sound of a vacuum cleaner. I actually had to make a sound file recording of it and it quieted her right down. I heard later that it mimics the sound the baby was used to hearing in the womb, so it's rather fascinating when you think about it.
Well, there *was* a second thing that worked and I've heard others saying the same... a car ride, but who wants to take a nightly drive just to stop a baby from screaming?!