Ode to a Nightingale - John Keats -
because the language is so lyrical and the poem exceptionally crafted in a technical sense. Also, it is along the same themes of Hamlet's "To be or not to be" (here, "Do I wake or sleep") soliloquy. But it's better. When Keats, dying of TB at the time it was written (which he diagnosed himself), speaks on this theme, it feels all the truer. He even makes death seem sweet in atotally non-morbid way.
The Love Song of J. Alfred Prufrock - T. S. Eliot -
because it puts into words what cannot be put into words; some vague notion of what it feels like to be a human, privy to aging and regret. It is unashamedly vague ("it is impossible to say just what I mean"). And it contains some of the greatest and most simple lines you'd give your arm to have written ("I have measured out my life with coffee spoons").
Can't think of a third at the moment, either Two Voices - Alfred Lord Tennyson, or The Road not Taken - Robert Frost.
Best poet, Keats. He is the archtypal pot inasmuch as he lived the poet's life (died young, unrequited love, travelled to and died in Rome, etc.) and wrote exceptionally poetic poetry - very lyrical.