Whenever I ask a friend about the symbolism of the Raven from The Raven, they always seem to say death.
Is that the only thing the Raven is meant to symbolize?
I don't believe the Raven symbolizes death at all, but rather life, in grief of having to live after a loved one is dead. As Poe himself put it in his essay Philosophy of Composition:
The reader begins now to regard the Raven as emblematical — but it is not until the very last line of the very last stanza, that the intention of making him emblematical of Mournful and Never-ending Remembrance is permitted distinctly to be seen
The phrase "mournful and never-ending remembrance" is the title of a biography of Poe. It's a theme Poe returned to several times, such as in Annabel Lee.
Of course authorial intent is only one factor to consider in interpreting a work; see this discussion. It does, however, jibe with my own understanding of the poem even before I read Poe's explicit thoughts on it.
The Raven is thus even sadder than death itself. The speaker craves forgetfulness, and will never have it: his heart shall be "lifted -- Nevermore". He could be content, or at least cope, with loneliness. But the Raven is a constant reminder: he lives not just with the loss but the knowledge of the loss.
Ravens, historically, represent two things.
One is death because of their association with dead bodies.
The other is knowledge, because they are distinctly intelligent birds. (For birds, of course.)
These two traditional symbolic meanings do cover the actions of the raven in this poem, without actions or elements that are left inexplicable without further symbolism.
Obviously the Raven does represent death. Since we know this, I will not touch on it here. However, there are a few possibilities other than that:
The raven in popular culture (described here) can symbolize many things. Ravens have a wide variety of roles in myths and culture; they can symbolize things from death and war to wisdom to creation of the world.
According many analyses I found while searching (including this one and this one), the raven also symbolizes the narrator's inability to do anything about his eventual fate; since the Raven is perpetually saying the same thing ("nevermore"), the narrator knows what the answer will be. So since the raven usually doesn't speak [citation needed], this is why he chose such a nonsensical animal.
In addition, the raven's perching atop the bust of Pallas might symbolize it's vanquishing of wisdom and justice.
The raven can also symbolize the devil; since the narrator thinks it is from "the Night's Plutonian Shore" and because it is described as a "demon."