"IT" has to be the scariest novel I have ever read.  Great character development, surprises, and terror - AWESOME!   Is anyone aware of any books that come close to this book?

Try  The Stand also by KIng.  Not as scary but it's my favorite King book.   I think most of the scariest books I've read are by King.

Try Pet Cemetary or The Shining.    Another author I really like is Dean Koontz.  His early works are more on the horror side. Try:  Phantoms,

Watchers and Lightening.  Lightening is more Sci-Fi/thriller and it's one of my favs.  Good luck trying to pick!!

I was going to say The Stand too!  Also Heart-Shaped Box by Joe Hill and Hell House by Richard Mattheson.

Here's a few older ones I like Deen Koontz's "Intensity". and also, Red Dragon is pretty bad as well.  I read a third of the book "It" and had to stop, since I'd seen the movie and couldn't get the freaky clown out of my head at night after reading and trying to sleep, lol!

I don't really scare easily, but if Stephen King scares you, then try anything written by Sarah Pinborough.  Her style is similar to SK.  I think that Breeding Ground might be a good first choice, but all of her books are fairly creepy. Four of her books are currently available in the system.  You might also like Christopher Fowler.  Spanky and Psychoville are my favorites, for what that's worth. *g*  Of the few currently available in the system, you might want to try Rune.  Roofworld is amazing, but it's not as scary as you're looking for.  CF also writes a detective series with Bryant and May as the main characters.  These are great books, but not horror, so unless you like that genre, too, you'll want to read the descriptions of the books before ordering.

ETA:  I forgot to add the best haunted house book I've ever read, Susie Moloney's The Dwelling.  Pretty scary and a great read.