Time for an update, I think.

1.) Alien (1979)
2.) The Shining (1980)
3.) Saw (2004)
4.) 28 Days Later (2002)
5.) Psycho (1960)

Runners-up are as follows;

6.) The Evil Dead (1981)
7.) The Thing (1982)
8.) The Exorcist (1973)
9.) The Last House on the Left (2009)
10.) The Texas Chainsaw Massacre (1974)

Mine hasn't changed much.

The Ring (2002)
The Shining
A Nightmare on Elm Street (1984)
Texas Chainsaw Massacre (2003)
Alien

- Audition
- A Tale of Two Sisters
- The Descent
- [REC]
- Noroi The Curse

1. The Shining (1980)
2. Alien (1979)
3. Halloween (1978)
4. The Thing (1982)
5. The Exorcist (1973)

1. THE TEXAS CHAINSAW MASSACRE

No blood. No supernatural creatures. Only humans.

The sheer terror I felt is unmatched by any other movie.

- Eden Lake, for the sheer reality it can represent
- Troll Hunter, because that movie is fucking underrated
- The Tunnel, because there are interesting elements that, if not original, sound fresh

1. Rosemary's Baby
2. The Shining
3. Alien
4. The Thing
5. Psycho

Honorable Mentions: The Exorcist, Hour of the Wolf

The Thing and Alien are incredibly similar so they're kind of interchangeable. The world in Alien is so great that I have choose it over The Thing even though the monster in The Thing is a cooler concept.

The Thing
Alien
A Nightmare On Elm Street
Scream
The Omen
Halloween

These are not necessarily the scariest horrors but rather the best movies that happen to be straight up horrors (although I'm not sure if Scream qualifies, it's more of a thriller so that's why I put one more on the list). The scariest list would be much different. It would probably be something in the vein of Ringu.