It is has some creepy moments but it's the disturbing nature of this book that always got me and that is always going to be Richard Laymon's The Beast House Trilogy. This guy had no problem getting to the punch and just being upfront. His monster was disturbing, some of the characters were not all that nice, others nicer and the situations can be desperate. He creates a real tension in his stories that never fails to surprise me.
Another I love is Stephen King's Misery. That was a wonderful little read, that kept me captivated from start to end.
This is not horror but more thriller but damn it deserves a mention. I'm currently reading a book by Dean Koontz called The Husband and almost finished, it's about kidnap, twists and shocks. Why does this deserve a mention? It focusses on very real aspects on our own lives, throughout the entire book so far I feel this could be something that happens to me and that is an unappeasing thought. How he manages to create such unique characters is to his credit and I absolutely think this is a disturbing but fantastic!! read.