You are refering to the traditionnal "auto" flash mode . Many flash manufacturer (SR electronics, Olympus, Phoenix , etc ...)offer slave flash for digital cameras (they ignore the preflash). These slave flash can have manual or auto mode settings just like "normal" external flashes. There were many threads about this subject in the external flash forums.
Myself, I use a normal external flash triggered by a cell, via a home made counter that ignore the first-secend-third preflash.