Ligeia

This one's also late.... This one was quite obvious about how it hinted about vampires. First off, there was the narrator's description of Ligeia: huge eyes, pearly white teeth, pale skin, raven black hair, knowledgeable above most others. She would enter a room and he wouldn't even realize it until she started speaking to him. Also, her family was an ancient, highly-respected line of people. This hints at vampirism do to the physical aspect, as well as the fact that since she knew all of the classical languages and everything, she's probably been around a really long time. The poem she recited on her death bed also hints at the fact that she knows what's coming, and it's not going to be eternal salvation. Once Ligeia dies, the narrator marries Lady Rowena, and he hates her. She doesn't love him, either. She gets sick mysteriously, and her doctors can't figure out what's wrong with her. She becomes over-sensitive to sounds and light (like vampires are). During her sickness, she drinks some wine which the narrator sees some 'ruby drops' fall into, but he can't fathom the source. One of the most obvious clues about vampires is the scene at her death bed, in which she keeps dying and then suddenly coming back to life. Eventually, she gets up and starts walking over to the narrator. At this point the narrator becomes suspicious and finds out that it is Ligeia, somehow manifested in the former body of Lady Rowena.
Out of the three works of Poe, this one most obviously points to vampires.