The Poetry Archive claims to be "the world's premier online collection of recordings of poets reading their work". The main page will open a RealAudio file whether you want it to or not, so you may prefer to explore the site from one of the inside pages, like the Historic Recordings page, where you can listen to Robert Browning (reciting "How They Brought the Good News from Ghent to Aix" and forgetting the words halfway through), Alfred Tennyson ("The Charge of the Light Brigade") or W.B. Yeats (sonorously declaiming "The Lake Isle of Innisfree"). Or if you want something more modern, there's Ashbery, Heaney, Logue, Pinter ..

Check it out here: http://www.poetryarchive.org/