What single book is the best introduction to your field (or specialization within your field) for laypeople?

So what if this has been bookmarked by 1,160 delicious-users and added as a favorite by 1,035 MeFites? It’s new to me.

My addition to this list would be Kenneth T. Jackson’s Crabgrass Frontier: The Suburbanization of the United States. It can get a little academic at times but I think it would satisfy a layperson interested in the history of the American urban form.

What would you add?