Watch a trailer for The Devil and Daniel Johnston I 'discovered' Daniel Johnston fairly recently and have been captivated by his songs, his singing too (though it's not for everyone) and other artists cover versions - Beck does a great version of True love will find you in the end - the documentary, which won at Sundance last year, looks interesting but I'd be a little worried that it buys into the he's a genius because he suffers from mental illness fallacy rather then he's a talented artist who battles against illness.
Daniel Johston the visual artist is also in the Whitney Biennial of American art this year.