We're reading "Ode to a Nightingale" tomorrow in English Lit. I don't know how it will turn out; I love this poem so much that it will be hard to avoid simply reading line after line, interspersing them with exclamations of, "Ohhh ... isn't that wonderful? Isn't Keats wonderful? Don't you love Keats?"
I decided to find a recording of a nightingale singing online (ah, the joys of technology!), so they would have an idea of what Keats was hearing as he wrote the poem. I found a wonderful web page, part of The British Library's website: Listen to Nature. You can click all kinds of critters from crocodiles to dolphins, to marsh frogs, to cicadas, to gorillas, to purring cats, to all kinds of birds--including the nightingale. In fact, you can listen to a 1910 recording of a nightingale, apparently the oldest known recording of such.
Be sure and listen to the musician wren, which has a beautiful birdsong. It's on the Wrens, Chats, and Thrushes page--which is where you'll also find the nightingale recordings.