What's the scariest movie you have ever seen? I mean can't sleep, gotta keep the lights on scary.
Mine would be Event Horizon.

I don't really know. Thrillers and gory movies never scare me, I guess movies that are really obscure or mind-twisters are the ones that unnerve me.
But I don't get easily scared by movies. (Games on the other hand... I just can't go into the water sometimes.)

Just a short list, probably have more:
Ring (Jap Original)
Ju-on(Jap Original)
Shutter(Thai Original)
The Shining
The Exorcist

Ohhh god, Ju-On nearly made me run out of my house. How is Ringu? Is it A LOT scarier than The Ring? How could I forget the Exorcist, my favorite was number 3.

Well, I love being scared in movies. Here are some of my favorite ones:
Blair Witch Project
The Ring
War of the Worlds (the beginning is one hell of a ride!)
Paranormal Activity
The Exorcism of Emily Rose
Fire in the Sky (terrorized me when I was a kid!)
[.Rec]
Jacob's Ladder
Signs
Silent Hill

There's a scene in Ringu 2 that I should not of watched alone, in the dark, when it was very cold. Not so much scary, but it did put me on edge for the night.
As a little kid (3-5), Gmork (Neverending Story) really scared me.

Blair Witch Project is a serious underrated movie, it is so scary if you watch and listen closely and pay attention to the story. [.Rec] got me good too, especially the last bit where they look down the stairs and all their friends are climbing up screaming their infected screams.
Paranormal Activity got me good too, but just the sounds and the screaming. You know they are making a Silent Hill 2? It is more closely based on the games, specifically Silent Hill 2 and 3 and 4.

legally blond 2
i still have nightmares.

Dude.. me too...
But
Bring It on....
has kept me awake time and time again...
Candyman.... had me pretty much jumping out of the shower every so often... My sisters were mean.... very very very mean....

You have to watch Shutter then. It makes The Ring look like Days of our Lives, and Exorcist like Barney and Friends. Ringu was more emotional than scary, but I liked it.

Well, the last scene of REC creeps me out (in the attic)
As did the blair witch project

Tomb Raider. I was scared because it was terrible.

Paranormal Activity
The Exorcism of Emily Rose

Definitely one of the most scary for me...
Candyman
Candyman
C...
Still can't do it!

There is a scene in The Exorcist 3 where a nurse is doing her rounds and the camera shot is static and gives a long view of the corridor., with the nurse entering rooms then coming back out and into shot. You know something is gonna happen but it still scared the crap outta me when it did.