What is your favorite poem?

I'm really enjoying catching up on my modern poetry class. I haven't done any poetry in a very long time, and I'm really getting a lot out of the class. I want to read a lot more poetry. So...

What's your favorite poem? I asked on FB too, but since there's a lot more room for discussion here, please feel free to get into why or any other poets & poems that you'd highly recommend. Thanks!