I think some of HP Lovecraft's better works should be added here, such as The Dunwich Horror, At the Mountains of Madness, Whisperer in Darkness, The Silver Key, The Dream-Quest of Unknown Kadath, etc. His poetry would also be a great addition. It's pretty hard to find (in my experience) though it is very good.

I'm almost positive that his work is in public domain. He's been dead for some time, and Ive seen a couple of other websites that have it.

I realize that Lovecraft may not have the same kind of reputation and literary recognition that most other authors on this site have, but his stories are really of an excellent quality. Many accomplished modern authors (Neil Gaiman, Stephen King, among others) consider him to be a great inspiration on their work.