The Poetry Foundation has put together a Learning Lab to help students discover more about the poem, complete with beakers and Bunsen burners. Just kidding.
The American Academy of Poets hosts a concise introduction to John Donne, many of his important poems, and a bibliography of his work, if you're hungry for more metaphysics. And who isn't?
Here's a helpful (if overly intellectual) introduction to John Donne and Metaphysical poetry.
The voice of Harry Potter's Aragog and the bad guy in Indiana Jones and Bond, Julian Glover looks out the window at the sun and recites the poem.
As part of their learning lab, the Poetry Foundation hosts a fine reading of the poem.
T.S. Eliot saved the Metaphysical poets from irrelevance with this important essay. Try on your tweed and get reading.
The Norton Critical Edition contains the most accurate text, excellent footnotes, and critical essays about Donne, if you really want to dive in.
John Stubbs's authoritative biography analyzes Donne's complex religious and romantic inclinations.