If you are an avid reader (of anything) and are not familiar with Project Gutenberg (http://www.gutenberg.org/wiki/Main_Page), you are doing yourself a great disservice. As they state on their homepage:
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As they state, most of these books are available because their copyrights have expired, making them usually quite dated. However, for anyone with a bent for the historical, Project Gutenberg is a gold mine. I did a quick search for “horror” on their website and received 169 titles in response. For a few, the only relation to the horror genre was the word “horror” in the title (such as “Southern Horrors: Lynch Law in All its Phases–which is a horrible subject, but is non-fiction vs. horror fiction). However, many are the classics or founding works of the horror genre, such as Frankenstein by Mary Shelley, Dracula by Bram Stoker, The Vampyre: a Tale by John William Polidori, The Castle of Otranto by Horace Walpole, The Strange Case of Dr. Jekyll and Mr. Hyde by Robert Louis Stevenson, Fantome de’l Opera (Phantom of the Opera) by Gaston Leroux, many works by Edgar Allan Poe, The Great God Pan by Arthur Machen, The King in Yellow by Robert W. Chambers, The Shunned House by H.P. Lovecraft, and many others.
Please take the time to visit this treasure trove of literature and of the horror genre, and if you are so inclined, please consider making a donation (via their website) to support their worthy cause.