there have been a few. But the ones that come to mind are:
Resident Evil 1 when the dog jumps through the window.
Dungeon Master 1 (on the Amiga) the sound of the footsteps when a monster was close. I got all involved and had the volume really high and turned corner and ran into a Mummy and when it screamed I did jump out of my seat for a second haha.
There was another Amiga game that I can't recall the name of (I know it was out on the mac too) there is a room with 4 coffins and again I had the volume super high and I opened a coffin and a demon jumped out and screams and disappears was another good jump scare.
I think the first honest "have to stop playing now" moment was after getting chased by the garagantua (stampy or w/e it was called) at the rail station in Half Life 1 (can't recall if it was original or Blueshift/Opfor), you can hear the big bugger coming up behind you and you have to run. My heart was beating, I was sweating bullets and just managed to make it. Hit esc, go for a smoke to calm down...
AvP as marine always freaked me out (funnily enough, I could play the alien no problem). System Shock 2's cyber nannies unmanned me as well..
SWTOR - Asmodai Mereel (Geek Legion) BFBC2 - Stabbitha TF2 - asmodai DDO - Azshaz (Ghallanda) WoW - Dys Others - AoC, WAR, FE, EQII, too many more to list
FEAR was the first game that really sent chills up my spine - especially when the violins started screaching and you knew something weird was about to happen.
Doom (orginal) was the 1st game that kept me from sleeping, mainly because I played it so much I would be thinking of running and gunning down corridors. To get to sleep I used to imagine sharing a beer and yarn with pinkie so that all was at peace.
I have to add my voice to the ones already calling it for Doom, but my first memorable scares came from a game that preceded it by a couple of years - X-Com (aka UFO: Enemy Unknown in some territories).
Any mission that took place at night (especially terror missions) could be intense. Like when you'd walk down a long alleyway and when you got to the other side you'd spend your last AP to turn around and OMFG THERE'S A CHRYSSALID STANDING RIGHT THERE! Or after a few quiet turns when you 'd maybe start to relax a bit, during the alien's movement phase a shot from a plasma rifle would come out of nowhere and take one of your guys down and you'd jump in your seat.
By the end of most terror missions my nerves would be shot and I'd be a gibbering wreck.
20 years later and I still break this game out to play through it a few times a year.
 Oh and that music! So creepy, man.
Last edited by Bam Stroker; 7th November 2011 at 01:35 AM.