The Cicerone guide was the first book I ever bought and read about the JMT. It is written by Alan Castle who has written many other guides as well. He is English and most of the Cicerone books are for trips in Europe so the book reads as if you are from overseas. It has tons of information that is great if you are traveling overseas to hike the JMT like insurance, public transit, money, and some "translations" from English to English. The first half of the book has a lot of good information about planing your trip. Everything from permit applications, regulations, food drops, and conditioning is covered. The second half is mainly a trail guide, broken into a twenty-one day, southbound itinerary. Each day has a very basic map, an elevation/milage chart (not graph), an overview of the day, and a more detailed description of the day. There is an elevation graph broken into 3 parts scattered along the guide as well. The itinerary I am planning on is loosely based on Mr. Castle's book. The book itself is bound in vinyl and is relatively small, so bringing it along is not too much of a hassle.
The Wilderness Press is an American publisher who makes some of the best backpacking and hiking guides I have read. Many of my training trips have been planned from their "Backpacking California" and "Backpacking Arizona" books. "The John Muir Trail" is written by Elizabeth Wenk. This book has the planning and preparation section at the front much like the Cicerone Guide, but it is less focused on prepping a foreigner for the US and concentrates more on the specifics of the JMT. The guide section is written for both a Northbound and a Southbound hike which was helpful for me in deciding what way to go. It breaks the hike down into 13 segments, usually ending on a major pass, drainage, or border. The author describes many of the plants and animals along the trail as well as gives some interesting history and geology lessons. Rather than lay out an itinerary, she just mentions where campsites are and which ones are really nice. There are some great charts in the Appendices, including one that describes the location of many established camp sites.
I really think that these two books complement each other very well and I would highly recommend that anyone who wants to start planning a JMT through hike read through both of these great books.