Stephen Wiltshire

I remember seeing something about Stephen Wiltshire years ago, he's a guy who can look at something, memorise it and draw it back in minute detail at a later date (sometimes a long time later).

He managed to remember the entire layout of Rome (via Kottke) after circling it once in a helicopter. He's also done Tokyo and Hong Kong. You can see some of his work online and buy prints or originals.