Here are a few suggestions for any enthusiast or aspiring writer of horror to read. This list contains not only horror novels and stories, but also books on grammar and other mechanics of writing and anything I think might be helpful. I am making no attempt to put these in order of priority. I may just write these down as a I think of them I will add to it occasionally, so this list will never be complete.
If you would like to see a lot of what I have read and would like to read, look me up at www.goodreads.com.
I start this list with the obvious condensed into one recommendation: anything written by The Four Horsemen of Horror (my term) Edgar Allan Poe, Howard Phillips Lovecraft, Stephen King, and Clive Barker.
“Supernatural Horror in Literature” by H.P. Lovecraft (even if you read nothing else under #1 above, read this for a summary of the history of horror literature up to Lovecraft’s time).
Frankenstein by Mary Shelley
Dracula by Bram Stoker
The World’s Greatest Horror Stories by Stephen Jones (Editor) and Dave Carson (Editor) This volume contains twenty-one masterpieces of horror as recommended by H.P. Lovecraft. All of these are noted specifically in his essay “Supernatural Horror in Literature”.
“Lukundoo” by Edward Lucas White (included in The World’s Greatest Horror Stories, but one that in my opinion stands out from the rest as one of the best).
The Writer’s Chapbook: A Compendium of Fact, Opinion, Wit, and Advice by the Twentieth Century’s Preeminent Writers by George Plimpton
I Am Legend by Richard Matheson
Psycho by Robert Bloch
The Island of Dr. Moreau by H.G. Wells
The War of the Worlds by H.G. Wells
The Martian Chronicles by Ray Bradbury (though science-fiction, this book is worth studying for its elegant use of English)
A Season in Hell and The Drunken Boat by Arthur Rimbaud (though not horror, these works are notable for their use of passionate language to describe the agonies and miseries of love and interpersonal relations).
The Inferno by Dante Aligheri
The Strange Case of Dr. Jekyll and Mr. Hyde by Robert Louis Stevenson
Heart of Darkness by Joseph Conrad
“The Illustrated Man” by Ray Bradbury
A Clockwork Orange by Anthony Burgess
An Occurrence at Owl Creek Bridge by Ambrose Bierce
Interview with the Vampire by Anne Rice
Silence of the Lambs and Red Dragon by Thomas Harris
Of course, I also recommend reading any of my works that are available on Amazon.
If you would like to start reading in any genre, one of the best ways I have found is to find an anthology in that genre and begin there. For that reason, I am listing here various lists of horror novels, short stories, and other works or links that lead to them. I am also including lists of horror films, because a good story is a good story whether on paper or celluloid. This page will be updated periodically, so check back often to see what is new. Also be aware that some of these links may be out of date.
Goodreads.com has a wide selection of various horror lists from Best Adult Vampire Books to Best of Little Known Authors to Best Gothic Novels of All Time.
The Greatest Horror Books of All Time [144 in total] by Ranker.com.
Wikipedia has an extensive list of horror films dating back to the1890’s.
Top Ten Horror Fiction for Youth by Booklistsonline
This is interesting: 10 Horror Movies Based on Actual Events.
25 Best Horror Novels by Listal.com.
Check out the Horror Writers Association’s reading list.
Go to the first page of The Horror Club and scroll down, keeping an eye on the right side. You will find a very extensive list of horror film lists organized by country, decade, genre, grade and several smaller categories. You could probably spend several years (I kid you not) watching all the movies in these lists.
Top Ten Horror Novels of the Year  by Bloody-Disgusting.com.
Ten Books That Will Scare the Sh*t Out of You by the Huffington Post.
Top 10 Horror by Spooky-Reads.com
Jones’ and Newman’s “Horror: 100 Best Books (Recommended Reading List)“. Wow! These guys go through the history of Horror back past Horace Walpole and Dante to Aeschylus. If you want to go through the history of horror, check this out and maybe review your copy of Lovecraft’s “Supernatural Horror in Literature”. That should give you a good start for a dissertation on the history of horror fiction
Here are also a few film lists to check out:
Top Ten Truly Disturbing Horror Films by Moviesonline.com
Check out the Best Horror Movies List.
Time Out London has their list of the 100 best horror films.