I was all set to do a write-in vote for Shirley Jackson, but you had her on the list, A! When I was about 9 or so I read this big thick compilation of all her works. Some of them were light-hearted and really funny. Some were really scary. Very confusing.
I also voted for Ira Levin (Rosemary's Baby, Boys From Brazil, This Perfect Day, and more), and Edgar Allan Poe. Although now when I think of his stories, my mind is overtaken by Bart Simpson saying, "Quoth the raven, 'Eat my shorts.'"