It's not a book on landscape photography, per se, but I would always recommend "The Negative" by Ansel Adams. It's where he details his zone system and is really a great overview on how to visualize the result you want in any photograph and then how to shoot to get that result. Obviously it long predates our digital processing flows of today and has a lot of detail on film photography, but most of it is still highly relevant and I think most interestingly, in his preface, he talks about how interested he is in the future where computers could be used to aid in realizing his photographic vision.
The Negative is definitely a great book, a must read regardless of the genre one shoots but even more so for landscapers.
About more specific books, I would say that for photo books it would depend on the style of landscape you favour - minimalist, ultra-vivid, classic, etc. Perhaps it could be useful to browse online, find some photographers you like and see if they have books out. Looking at other people's work is definitely a fundamental learning tool IMHO, especially if one takes the time to try and analyse their images, to find out why a photo is successful, what are the problems with it, mistakes, and so on.
About instruction books, I don't believe one can learn landscape photography from a book, sorry. You can definitely learn the basics of photography, which are in the end extremely simple, and the workings of your own gear, but then my recommendation would be to go out there and experiment in the field, either alone or by joining Workshops.
Two of my favorites are " Mountain Light" and "Galen Rowell's Inner Game of Outdoor Photography" both by Galen Rowell. They were written before digital so technique is a bit dated but I enjoyed the essays and philosophy within.
