While I agree that the narrator of the poem is a character and that Lenore's presence, although not physical, is certainly important to the poem, I'm not sure I believe the raven counts as a character. To consider this alternative, we might entertain the idea that any quality, tone, or meaning the raven seems to possess only occurs as a result of the narrator's imagination and not because the raven itself intends it.
The raven's one word —Nevermore — is, at first, interpreted by the narrator to be, simply, the word that its master must have uttered over and over, and this is a perfectly logical explanation of the bird's speech. If, as the narrator suggests, the bird is a messenger, something sentient, and a being with knowledge of another world, then the raven is a character. If, however, the raven is like the rest of its species and just happened to fly into the narrator's open window, then I think one could argue the raven doesn't count as a character any more than the bust of Athena or the narrator's books do.
If the raven is a character, then we would likely classify the conflict as one that occurs between the narrator and the raven; it seems just as likely, though, that we would classify the conflict in this story as an internal one. In this case, the bird seems to be the antagonist, but only as a result of the narrator's internal conflict. This would make the narrator's inner conflict the poem's antagonist. The narrator projects his fear that he will never see Lenore again onto the raven, scapegoating it for fears he already had.
The characters in "The Raven" are only the speaker and the bird. The speaker is alone, and it can be assumed that he wants to keep himself in isolation. The speaker is kept in the grip of grief from the loss of his love, Lenore. He seems to want to be kept company with only his memories and his grief over Lenore.
While Lenore is not physically present in the story, she is definitely a presence.
The speaker discusses the many wonderful qualities, as well as his inadequacies, basically to himself, but the raven does respond to his laments.
The characters are the speaker, the raven, and Lenore. Even though Lenore is not alive she is an important person.