What are the scariest horror novels?

I read the novel "Swan Song" by Robert McCammon when I was ten. Loved it. It is often compared to Stephen King's 'The Stand" because of similar premises, but I find it to be the better of the two books (and I like King's work). It taps into the old Cold War fears of Nuclear War and how vile people become in times of desperation. I recommend it.

I came here after seeing the thread's title to write, "The Exorcist." I've never read it, and the movie costs me months of lost sleep. When the original film came out in the 1970's, my parents were at a party for a Catholic College event, and ended up meeting one of the priests who was at the actual event the novel is based on. At the time, this priest had recently finished his seminary training and was a college football linebacker, when he received a call from his higher-ups who told them they were sending him on  a unique assignment. They said it was a 12 year old boy (not a girl, like in the film) and all his only duty was to physically hold the boy down to prevent him from harming anyone else in the room. This priest was apparently a brutal linebacker on the field and said that the kid was the strongest human being he had ever physically faced. He was chosen for the position, specifically because of his size and football background. My parents were asking him all kinds of questions, but there's one that really stands out that they told me. The priest said when they would first start the exorcism ceremonies, the boy would suddenly pee from 20 feet across the room and hit whoever the prayer was right in the eye.

The shining was pretty scary when I read it.

Yeah that was a great novel. 
The movies are campy fun, though.

Fun fact: Stephen King was intially not even going to even have the book published, believing it was too dark and disturbing for most readers.

The Exorcist was a terrifying, and also a depressing read.

There were several instances that could have been incorporated into the film to add to the shock.

In the novel, Captain Howdy would chase Regan through the home and assault her. It was terrifying and depressing to read about a 12 year old girl physically harassed by an unseen entity.

This is not a scary/non-scary novel, but something we can all relate to. PDF Link at the bottom. Read it, love it, and laugh.

It began as a mistake.
It was Christmas season and I learned from the drunk up the hill,
who did the trick every Christmas, that they would hire damned
near anybody, and so I went and the next thing I knew I had this
leather sack on my back and was hiking around at my leisure.
What a job, I thought. Soft! They only gave you a block or 2
and if you managed to finish, the regular carrier would give you
another block to carry, or maybe you'd go back in and the soup
would give you another, but you just took your time and shoved
those Xmas cards in the slots.
I think it was my second day as a Christmas temp that this big
woman came out and walked around with me as I delivered letters.
What I mean by big was that her ass was big and her tits were
big and that she was big in all the right places. She seemed a bit
crazy but I kept looking at her body and I didn't care.
She talked and talked and talked. Then it came out. Her
husband was an officer on an island far away and she got lonely,
you know, and lived in this little house in back all by herself.
"What little house?" I asked.
She wrote the address on a piece of paper.
"I'm lonely too," I said, "I'll come by and we'll talk tonight."
I was shacked but the shack job was gone half the time, off
somewhere, and I was lonely all right. I was lonely for that big ass
standing beside me.
"All right," she said, "see you tonight."
She was a good one all right, she was a good lay but like all
lays after the 3rd or 4th night I began to lose interest and didn't go
back.
But I couldn't help thinking, god, all these mailmen do is drop in
their letters and get laid. This is the job for me, oh yes yes yes.

www.kkoworld.com/kitablar/carlz-bukovski-poct-idaresi-eng.pdf

The book that scared me the most was Salem's Lot by Steven King.