Unaussprechlichen Kulten
For those that don't know, the Unaussprechlichen Kulten is a fictional book from Robert E. Howard's short stories, and was later referenced by H.P. Lovecraft, so you know it's got some dark mojo. It was built by Vitreolum as a companion piece to his Necronomicon. That's the beginning of a pretty bleak, but damn cool library.
Original author: Tommy