The sermon delivered by the preacher is a passage from Poe's short story, "The Imp of the Perverse".
Fortunato, the drug company controlled by the Ushers, is the name of a character in Poe's "The Cask of Amontillado".
Prospero is named after the protagonist in "The Masque of the Red Death", another Poe short story. Similarly, Lenore's name comes from his poem, "The Raven".
Leo Usher and his partner own a black cat named Pluto. That is the name of the protagonist's feline pet in Poe's short story "The Black Cat".
"A Midnight Dreary" is from the opening line of Edgar Allan Poe's poem "The Raven," first published in 1845.