Gerard's Game by Stephen King actually made my tummy flip over with fright at one part
Also The Shining, the Dark Half, Pet Cemetary...SK usually does it for me if I want to be spooked
Have never really found any other author quite as scary as him, but will be orderng some of the ones mentioned here from the library
Oh, apart from the book of 'The Amityville Horror' - actually gave me nightmares 