The "villager rush" near the beginning of RE4. I actually screamed "HOLY SHIT!" when that happened.
Oh, and pretty much any part of playing AvP as a human. That game was 98% "HOLY SHIT!" because you just knew you were about to die a horrible, bloody death.
Honorable mention to Condemned during the walk to the farmhouse when you get bum's rushed by 4-5 big ugly tank motherfuckers who want you for lunch.

Or check out my new webcomic: http://selfcentent.com/







