The Scariest Books Ever

With another Halloween come and gone, it seemed a perfect time to reveal the Scariest Book I have ever read:

The Shining by Stephen King - Not sure why this book was so scary when I read it until I realized that haunted houses / creepy isolation terrify me.  This book is naturally a combination of the best of those two things so it makes sense it would be pretty scary to read...alone...in an old house...at night.  For my money this is the most terrifying novel King has written.  You have been warned. 

The Hot Zone by Richard Preston - A non-fiction thriller about a highly infectious African disease that kills up to 90% of those infected?  No idea why this would be scary, no idea at all.

Summer of Night by Dan Simmons - The main reason this one was creepy to me was because it reminded me so much of my friends and I hanging out during the summer.  This sort of thing (well, not all of it) could have happened to us.  Sure it goes slighly off the rails near the end but that does not take away the full effect of a creepy and dark summer horror.

It by Stephen King - A classic horror story that meshes every single scary thing into one giant stew of terror: evil clowns, monsters, and of course a giant freaking spider.  This is also a great book and one of King's true masterpieces (along with The Stand and The Shining). 

Bedbugs by Ben Winters - Winters set out to write a modern version of Rosemary's Baby and succeeded in writing a very, very scary novel about creepy crawly little bugs and losing your mind.  This is a taunt, top of the line novel.  Read it and prepare to do a lot of scratching. 

What other novels should I read to add to this list?