Ooo, this is on my pile to get to sometime. This inspires me to get to it sooner!
Cujo and Misery both freaked me out when I was younger, and The Sparrow, while not scary per se, had a level of creepiness as things were revealed.
Nightflyers: a haunted spaceship complete with exploding heads, reanimated corpses and the mysterious unseen ship captain.
Fevre Dream: vampires on a 19th century riverboat.
Do not read after dark.
The Exorcist, with Ghost Story by Peter Straub coming in a very close second.
I read the latter at the beach - lounging by the ocean in a recliner at a most tranquil setting. And I was scared to damned death while reading this book!
The Mist, which is also being made into a movie, directed by Frank Darabont, who previously directed The Green Mile and The Shawshank Redemption. I’m keeping my fingers crossed, because this is one of my all time favorite King stories.
Huh. Although I enjoyed it very much, I didn’t find Fevre Dream particularly scary. Fascinating, gripping, eventually touching. But not scary. 
Oh, I’m listening to *Heart Shaped Box *by Joe Hill right now, and so far it’s very good and creepy. It jumps right in to the scary stuff, it’s not shy. And I think I see some interesting threads already being woven - we’ll see if it maintains the level it sets up in the beginning.
And, yes, I have to agree that “The Color Out of Space” is dynamite. So is “The Rats in the Walls.” Come to think of it, I read both in My Favorite Horror Story, an excellent compilation by leading horror authors.
Oh, crap. Another addition to “Movies auRa would reeeeeally like to see but won’t because she’ll be hiding her face behind her hands the whole time”. 
The Turner Diaries… Because he meant it.
And “I have no mouth but I must scream” Not a book and not exactly frightening as horrifying. Still haunts my dreams.
Not the scariest book, but the opening chapter of Rose Madder didn’t do me any favors - and it wasn’t even a horror scene, just horrible.
As far as “scariest book” - other than stuff I read as a kid (and forgot), the scariest I can think of is Pet Semetary.
Oh! I, too, read The Exorcist at an age that no mother would approve - I was 8.
“Ghost Story”…while I’m not sure I liked the book all that much or think it was particularly good…did seem to sneak up on me and freak me out more than any other book I have read.
Oh Jesus Christ yes. The first one wasn’t too bad, but the 2nd and 3rd freaked me right out. I had to give the books away to make sure I’d never read them again.
The Stranger Beside Me Many people think Ann Rule got the job because she knew the serial killer, but her contract to write this book was signed before Ted Bundy was even a suspect.
Dracula is actually quite scary. You get quite invested in the characters, because it is mainly told through their diaries and letters to each other, and it is really well-paced–not a lot of jump scenes, but a lot of slowly growing menace.
The Hot zone was rather disturbing, as were the “Superflu” sections of The Stand by Stephen King, the religious-crap at the end of the book bored me, but the depiction of Captain Trips was quite unsettling…
Like a lot of you, I came in here to say this as well.
Mostly because my sister *works * at USAMRIID. Through all the containment, her office is appx 200 ft or so from the Ebola virus.
FYI, the actual building is **not ** as impressive as the book makes it out to be. It looks like an old high school in some places.
I have signed copies of both Hot Zone & Demon… 
Agree! Seems silly now but at the time I was reading it I got seriously creeped out. Even more so because, years before I read it I had a very memorable dream that had a lot of “abduction” elements to it.
Two collections I read as a child seriously crept me out. Both were edited by August Derleth, but the only title I can recall now is Who Knocks?
Mein Kampf, by Adolf Hitler. I read only about five pages many years ago, and it still gives me occasional sleepless nights.