"The Rest is Noise" by Alex Ross is the winner of the The Guardian First Book Award 2008. It is a non-fiction book, an history of 20th-century music to be precise.
Personally, I think that fiction and non-fiction should be separated in literary prizes. You cannot really compare them, and while some people read only fiction, other people prefer essays.
Also, I was disappointed that A Case of Exploding Mangoes or A Fraction of the Whole did not win, because I'm really looking forward to read them (apart from the fact that the second "puts me down" as it's 700-pages long and I'm biased against long novels).
These were the other contestants: A Case of Exploding Mangoes by Mohammad Hanif (Pakistan), A Fraction of the Whole by Steve Toltz (Australia), God's Own Country by Ross Raisin (UK) and Stalin's Children by Owen Matthews (UK).