Terry Pratchett: His World  - Stephen Briggs
I wasn't lucky enough to see the Exhibition but this is a great book about the world of Pratchett. The book includes timelines which detail not only Pratchett's life but also awards and first meetings with people he worked with.

The illustrations are beautiful and you get a better sense of Pratchett as the artist as opposed to just literary artist. It includes glimpses into his library as well as his work habits.

The last section is a look at upcoming Pratchett based projects.