What literary devices are used in the text? Provide examples of each.

Certainly, Poe uses mood to great effect in the story, making word choices that convey the gloom and moroseness of the house and landscape.  Details about the "clouds [that] hung oppressively low" over the "singularly dreary tract of country" before the description of the "melancholy House of Usher" help us to feel the gloom and sadness—even the rankness of the house—as the story's rising action is just beginning.
The narrator compares the sight of the house to the soul's depression that accompanies the "after-dream of the reveller upon opium—the bitter lapse into every-day life—the hideous dropping off of the veil." Here he seems to compare—via metaphor—the feeling of seeing the House of Usher to the experience of coming close to death.  In addition to employing this comparison, these lines continue to contribute to the foreboding mood: nothing good can happen in this place.
Poe employs imagery when the narrator describes his second view of the house—from a hill above.  He has allowed his imagination to run away with him:

An atmosphere peculiar to [the mansion and grounds] and their immediate vicinity—an atmosphere which had no affinity with the air of heaven, but which had reeked up from the decayed trees, and the gray wall, and the silent tarn—a pestilent and mystic vapor, dull, sluggish, faintly discernible, and leaden-hued.

This visual and even somewhat olfactory description of the grayish, heavy, disease-like mist presents a vivid image that sets the scene and further contributes to the mood.