Another thing I found was a link to the article on Horror Fiction.
It contains this group of authors:
* V.C. Andrews * Jay Anson * Clive Barker * Algernon Blackwood * Robert Bloch * Ray Bradbury * Ramsey Campbell * Nathaniel Hawthorne * James Herbert * Washington Irving * Shirley Jackson * M.R. James * Brian Keene * Stephen King * Dean Koontz * Michael Laimo * Richard Laymon * Bentley Little * H.P. Lovecraft * Arthur Machen * Richard Matheson * Robert R. McCammon * Joyce Carol Oates * Edgar Allan Poe * Ann Radcliffe * Anne Rice * John Saul * Darren Shan * Mary Shelley * Robert Louis Stevenson * Bram Stoker * Peter Straub
-V.C. Andrews is famous for writing "Flowers in the Attic", a best-seller about (I think) child abuse. I haven't actually read it, but I'm under the impression that most of her books after that (and she's had a long, lucrative career in the bestsellers lists) aren't worth the paper they're printed on. Try the original, at least.
-Clive Barker is like a really really dark Ray Bradbury, blending horror and fantasy to great effect (not to mention sex, violence, and crazy surrealism). Barker's incredibly creative, he has a great sense of humor, and his voice is one of the most original I've read. He writes stories that nobody else has ever thought of--a breath of fresh air. He isn't always good, but he's always exciting and unpredictable. Try his "Books of Blood" and go from there.
-Robert Bloch writes thrillers and noirs, damn good novels all. One of the things he pioneered was writing from the perspective of the killer (or lending sympathy to them). Try "Psycho" (the basis for the Hitchcock movie) and "The Scarf" for a taste of what he's about.
-Ray Bradbury (dunno how you don't know him, but you didn't mention him...) ... Ray Bradbury has been writing books and stories for, like, a hundred years. Some people don't like him; I love most of his stuff. Fahrenheit 451 is one the best books out there, period; Something Wicked This Way Comes is amazing and beautiful in its way; and there are so many great short stories out there. (Not to mention stuff like Dandelion Wine and The Martian Chronicles....) He's impossible to peg down; calling him a horror writer doesn't really do it. He generally writes fantasy, but not always; often he blends fantasy and horror and science fiction together at once. His prose is lyrical, moving, and energetic--he's older than God but somehow still writes like his heart is 12 years old, still possessing a boundless capacity for imagination and wonder.
-Ramsey Campbell is weird. I haven't read enough of him, but what I have read is very dreamlike--horrific, unexplained, arresting, absolutely original. His stories are entirely like anything else I've read, and closing the book is like waking up from something, you're not sure whether it was a dream or a nightmare. I recommend "Scared Stiff", a short story collection connecting sex and horror in some very interesting ways.
-Nathaniel Hawthorne lived in the 19th century, and in addition to inflicting "The Scarlet Letter" on generations of groaning high school students, he also managed to write some early ghost stories and a few Gothic novels (most notably, "The House of Seven Gables", which influenced H.P. Lovecraft). Haven't read any of his horror--I was one of those students.
-James Herbert is a pulp British author with an eye towards the macabre, the grotesque, the violent, and the darkly ironic. I haven't been able to get into most of his oeuvre, but I found a copy of "The Fog"--about a miasma floating around England making people go violently insane--and loved it. He may not be great, but he's certainly great fun.
-Washington Irving is the author famous for, among other things, the stories of Rip Van Winkle and the Headless Horseman of Sleepy Hollow. Read 'em if you haven't.
-Shirley Jackson you say you know (who hasn't read the Lottery?), but you might not have heard of her best novels: her last, "We Have Always Lived in the Castle", and her finest, "The Haunting of Hill House". The latter is an utterly chilling, brilliant, ambiguous story about a group of paranormal investigators in a supposedly haunted house. It's one of the best books I've ever read. (Short and cold--like an icepick to the heart. Emminently readable.)
-M. R. James is another classic ghost story author who influenced H.P. Lovecraft and Stephen King (among others; for an example of King's, look at his early story, "Jerusalem's Lot", in his collection "Night Shift"). So important that they call a certain kind of English ghost story "Jamesian". Might be available on the 'net, as the copyrights have probably run out.
-Brian Keene I know almost nothing about. He's a very new author, has won the Bram Stoker award twice, and seems fairly prolific.
-Koontz. Um. Don't.
Skipping ahead a bit....
-H.P. Lovecraft. I haven't read enough of him myself, but he's influenced just about everybody who came after him. Funny you should mention what Tolkein did for fantasy--Lovecraft did the same for horror (in perhaps a less destructive way). For a primer, go read "The Colour Out of Space" and "The Call of Cthulu"; both are available free online (along with most of Lovecraft's stuff). He didn't really succeed as a novelist, but his short stories built a world in which terrifying gods stood ever poised to destroy humanity; in which people had no way to understand these powerful forces; in which evil was seen obliquely--anything more and insanity was the inevitable result. So good that people carried on (and continue to carry on) the mythos in their own work, adding and homaging left, right, and center.
-Richard Matheson is, quite simply, fantastic, and helped to invent the modern horror story. A lot of his stuff is fairly famous. His best work might be "I Am Legend", a very original and meaningful take on vampires; he also wrote "The Incredible Shrinking Man" (a lot less hokey than it sounds), "Terror at 20,000 Feet" (made famous by the Twilight Zone episode) and countless other novels and short stories. (He does sometimes work in more of a fantasy bent; for example, his novel, "What Dreams May Come", about the afterlife. Also made into a pretty good movie.) He's incredibly prolific and it's basically all good, especially the short stories--Matheson definitely isn't afraid to experiment with a story.
As a side note, his son, Richard Christian Matheson, is a master at crafting extremely minimalist horror stories. (As an extreme example, he once wrote a story using nothing but one-word sentences.) His collection, "Dystopia", is absolutely fantastic.
-Anne Radcliffe is one of the people who invented the Gothic novel at the end of the 18th century. Her most famous is "The Mysteries of Udolpho"; it's good to read at least one of hers to get an idea about how the genre began.
-My cinema professor last semester said of Anne Rice, "That woman had just one book in her!" and it's true. Boy, is it a good one though. If you're one of the rock-dwellers who hasn't read "Interview With a Vampire", go read it now. (No, the movie isn't good enough.) It's an absolutely fantastic re-imagining of the entire vampire mythos--namely, vampires who don't like being vampires. Brilliant, rich, and well-written. Don't bother with anything else she's written, though, unless you absolute must know more about the characters (especially Lestat).
-John Saul is... well, bad. Hard to say more. He is occasionally interesting--The Blackstone Chronicles are pretty cool, for dealing with ghosts in an abandoned insane asylum (you just don't see that these days)... But do yourself a favor and rent "Session 9" instead. Give the rest of his stuff a miss--at the very least, there are plenty of better authors on this list.
Shelly, Stevenson, Stoker...
-Peter Straub is, frankly, brilliant. And terrifying, too. Besides his work with Stephen King (The Talisman, Black House), he created an excellent atmosphere of intensifying dread in "Julia", published a ripping good homage to the Gothic novel called "Ghost Story" ("Tell me the worst thing you ever did." "I won't tell you that, but I will tell you the worst thing that ever happened to me. The most dreadful thing..."), and wrote some bloody terrifying short stories to be found in "Houses Without Doors" (the best of which is "A Short Guide to the City", which... well, I won't spoil it).
Want more? Koji Suzuki, who wrote the "Ring" trilogy (which eventually became the excellent American horror film), does a fascinating thing by looking at the same basic story through the lens of different genres--first horror, then a little science fiction, then some very "high" science fiction. All of them are complex, original, and well-written.
Further suggestions can be found in Stephen King's excellent treatment of the horror genre, "Danse Macabre"--check his list of 100 important works between 1950 and 1980--and then go read the book too, okay?