Carlson's Guide to Landscape Painting by John Carlson
This is by far the best and most read landscape book I own.
I think I have read through the entire book a few times and then there are some chapters, like the one on trees and clouds that have been read multiple times more. Carlson weaves in practical advice along with his thoughtful sense of beauty in regard to the landscape.
If you are at all interested in learning to paint the landscape, this is a must read.
Most images are black and white, with some wonderful value diagrams. I even use some of his ideas about value and perspective with my still-life paintings, in order to achieve more atmosphere. A technique I would never of learned if it was not for this book and trying my hand at landscape painting.