LOL! Yeah the Oompas scared me too! I think the scariest book I've ever read was "Gerald's Game" by Stephen King- I read that in brightest daylight and it about near scared the pants off me!
"Flowers in the Attic" ~let's just say I had nightmares after that. I read the sequel, and couldn't deal with the sickness in it.
"Sybil" ~not really a scary book, but it's creepy to read about a woman's 16 personalities and the abuse/horror she suffered as a child. (Sally Field did an excellent job as "Sybil" in that movie!)
Mustn't forget the importance of atmosphere. When I was about 14, my mom was out of town for the weekend and I was home alone. So, I sat down on the sofa Friday evening with all the lights off except the one lamp I was using to read and opened Pet Semetary by Stephen King. I finished it about 3:30am and sat there watching the shadows, afraid to move until dawn.
All it would have taken was for someone to have let a cat into the house and I would have probably had a serious breakdown.
I cannot remember the name of the book, and it was several years ago I read it, but it contained true stories of some very weird and scary things...and I guess the fact they were true made nightmares for me! I think I hid the book so it couldn't be read again.
Yeah, Dean Koontz seems to always have a logical, scientific explanation for the things in his books which makes them at least plausable and so more creepy. Of course, I've only read about 6 or 8 of his books so I can't speak for them all.
Lightning is my all time favorite DK book. I wish they would make a movie out of that book. I'd go see it 10 times at the theatre then buy it as soon as it hit DVD.