Who's on the Mount Rushmore of American horror fiction?

Knowing I wouldn't finish because it's due at the library today, I jumped ahead in "American Fantastic Tales" and read some H.P. Lovecraft's great "The Thing on the Doorstep" (after skimming through a tedious story about a minister who mesmerizes members of his audience, leading them to commit suicide, ugh). It's obvious that Poe and Lovecraft form the two bookends of this volume, the two faces on the Mount Rushmore of American horror fiction in its first phase. Lovecraft is by no means the best writer in this volume. His best stories and novels obviously cannot touch The Ambassadors, Death Comes for the Archbishop, The Age of Innocence, The Great Gatsby - to name some of the greatest accomplishments of the other American writers who tried their hand and horror/fantasy/scifi. But Lovecraft, to his credit, devoted himself to this one genre, he developed a vision of the world that is uniquely and distinctly his own - which really what we ask of any great writer. Just reading a few pages of Thing on the Doorstep will tell you right away that he's not writing about a single strange event or a curious "tale," but that he has envisioned a world of such overwhelming strangeness and disturbance that it threatens the boundaries of sanity - his and ours. And I'm not talking about life on some other planet, life among aliens, or any of the farther reaches of science fiction. No, Lovecraft's world is ours, the people are real - but sad, loners, misfits, suffering from fear, and in touch with strange and dark forces that may, who knows?, exist all around us but of which we are totally unaware. He can take a setting or a place that most would consider ordinary and benign - he writes often about his native city, and my current home (workplace), Providence - and make it seem so strange and gothic that I don't recognize it, but when I walk the streets and think of him I cannot help but shudder. I'm not a huge devotee of the horror genre, but there's no doubt that Lovecraft is among the greats.