This is a loaded question, but what video game(s) scared you most?
I've played my fair share and I can't wait to get into the new lineup of survival horror games later this year/into '09 (RE5,L4D,Dead Space,etc...).

For me, I'd have to say that Resident Evil 4 is a masterpiece. I played that game and beat it like 5 times, it was addictive and interesting, and I loved it! For me to play a game more than twice after beating it is rare.

The first appearance of the "chainsaw guy" scared the crap out of me. I remember anticipating a chainsaw wielding maniac (after all, he was featured on the cover of the Gamecube version), but i had no idea where he would appear. After a cutscene and save in that house I walked outside and he ran up to me and sawed off my head before I could even blink.

Upon restart, my heart started beating rapidly. Here I was sitting in front of my TV with all of the lights off and the volume cranked and I thought I might soil myself over this animated character in a video game. I reloaded, went to the front door and activated the "chainsaw guy" as soon as he began running at me I freaked and ran back into the house and raced up that flight of stairs, freaking out. As I sat on the top of the stairs and tried to figure out what to do next, the unthinkable happened, he came in the house and raced up the stairs after me! I think I shot him down the stairs with the shotgun until he was dead. I thought about doing it again (since I had just saved) and try killing him outside, but I figured..."What the heck, it is a survival horror game, and I survived that encounter".

That scene (and the game overall) rocked! It was pure cinematic horror heaven spewing from my television and "innocent" looking Nintendo Gamecube. I actually cared about what happened next. If I wasn't playing the game I was at work thinking about it and wondering what would happen next.

That to me is the sign of a great game - you're playing it in your head when you're not physically playing it. I did that with a number of games recently (Bioshock and Dead Rising) and I wish more games affected me like that. They pull you in and scare the crap out of you!

Who needs lame Hollywood horror movies when we can play games like this?

all the resident evils before re4

The bathroom scenes in both REmake and Eternal Darkness.

The dog-through-a-window bit of REmake.

Much of the rest of Eternal Darkness.

Some other scenes in REmake (sharks in the water, those blasted chimera jumping out at you... the first sight of a hunter, and the crimson head under the graveyard)

The first moments inside the first building on the Island of RE4.... I wouln't say the rest of the game is scary at all, I like you was killed with my first chainsaw encounter (First I saw of him was after the first meeting with Mendez... just outside that house) but it wasn't a particularly scary moment.

Oh yeah, I forgot about Eternal Darkness. That was a GREAT GAME!
I liked how it would mess with your mind while playing.
Also, there were plenty of scares and creepy moments in both Condemned games!

Crimson zombies in Resident Evil remake. Hearing them scream for the first time, watching them sprint at you and then realising they can follow you through doors. To much all at once when low on amo and health.

The first Silent Hill. I used to absolutely hate when it would turn into the Otherworld, especially outside areas. I would run through them as fast as I could without stopping.

Then I played it high and it just seemed hilarious instead of scary. I would wait for the demon dogs to jump at my guy, then hit them with the lead pipe like baseballs. I couldn't take them seriously after that.

I was also surprised when I first played Bioshock. I thought it would be an action shooter. The mood was much tenser and creepier than I was expecting.

 This +

the first Condemned

FEAR

Uncharted....

because I avoid all horror games like the plague

some scenes in Eternal Darkness, especially when your sanity meter is low, some parts were just unexpected.

CONDEMNED!!!