There mere repetition of the word "Nevermore" by the raven can be considered ironic in literary terms, which allows for more expansive use of the phrase than the regular definition of "irony" might allow. Whereas "irony" in normal usage refers to the appearance of the opposite of what is expected, in literary terms it can have many meanings. By having the raven repeat the response "Nevermore," Poe is employing the use of abstraction as a form of irony; the word doesn't really have any meaning, unless the bird can be considered a messenger from the lost Lenore or, perhaps, it originates from within the narrator's mind. This is, after all, Edgar Allan Poe, a writer for whom psychological horror is more pronounced than physical horror.
Another use of irony involves the introduction of a bird where the reader would logically anticipate another form of life. The narrator, napping in his study is suddenly disturbed by a gentle rapping at his door. "Tis some visitor," I muttered, "tapping at my chamber door -- only this and nothing more." Deep in thought and apparently remorseful regarding a lost love(?) ["the rare and radiant maiden whom the angels name Lenore"], the stage is set for the use of irony in the discovery that the tapping at the door is not from a human visitor, but from a large black bird, the raven.
One of the more striking uses of irony is a quick, almost imperceptible reference to a figure from Greek mythology, Pallas. In relating the raven's movements within the chamber, the narrator describes the scene as follows:
"But, with mien of lord or lady, perched above my chamber door - Perched upon a bust of Pallas just above my chamber door - Perched , and sat, and nothing more."
Once again, the narrator is described as emotionally devastated by the loss of Lenore. In Greek mythology, one reference to Pallus is a Titan killed by Athena, the goddess of reason, intelligence, arts and literature [it bears reminding at this point that the scene takes place in a study within which the narrator is contemplating "a quaint and curious volume of forgotten lore"]. That the study should include a bust of Pallas, and that the raven should choose that location upon which to perch, presents a scene of supreme irony. The narrator, like Pallas, as been "killed," emotionally if not physically, by a woman.
As point of view in itself constitutes a form of irony, then Poe's use of a narrator, common in his writings, in "The Raven" qualifies as another use of irony in the poem.