David Morley flagged this up earlier on Twitter, and it's absolutely fascinating. It's Jacob Polley's poem The Reader, draft by draft, or at least in umpteen alternative versions.
At StAnza recently, one of the highlights for me was Paul Farley's workshop in which he took us back through the drafts of his poem Treacle. I thought it was really a pretty brave thing to do - I think I'd die of shame if some of the drafts of most of my poems ever saw the light of day. It was actually quite reassuring to see that the simple hard graft of writing and revising again and again could be so effective, but also slightly terrifying in the way it highlighted that changing just one or two words could tip a poem in a completely new direction.