Recommendations sought: Books, nonfiction

[vakkotaur]

For the last few months I've been reading the various books in Terry Pratchett's Discworld series. They're rather entertaining and Pratchett manages to make a few points that apply to the real world. I've finished with all the Discworld books so far published, as far as I know. Right now I'm going through Good Omens, a book co-authored by Terry Pratchett and Neil Gaiman. I'm taking my time about it, but expect I'll finish it in a week or so and then I'll be done with Pratchett for a while.

I also want to get away from fiction for a bit. Any recommendations for non-fiction? The one big restriction is that I will be specifically avoiding any overtly political text, at least anything within the last decade or so. I know I'm leaving the field fairly wide open, that's intentional.

So, what book(s) should I look into and why?