hmm.. no one said the obvious choice of bach's Toccata and Fugue in Dm, also Fantasia and Fugue in Gm, Fantasia's BWV 561-563, I wonder what some of his other really creepy works are though.
come on, lets hear some more crypt/haunted house/mad genius/sinister/halloween esque suggestions! prehaps ones playable by intermediate players, all this liszt and rachmaninov is scaring me enough in its technical aspects!