There are now an immense number of books about NLP available by a variety of different authors. I am sure that many of them are very good but I am simply not familiar with most of them. The list below contains mostly the standard classics, written by members of the original group of developers of NLP. There are a number of other good lists of NLP on the web now, much more extensive than this one.
(For one somewhat more extensive list of books, along with some reviews, check the web site maintained by Stever Robbins. Another good list is at Merle's World.)
The first and most basic of the NLP books is The Structure of Magic, vol. 1 (Meta Press, 1975), which most people also find the most unreadable of all the NLP books. It's probably not the place to start (except for those with a knowledge of transformational grammar) but anyone with a serious interest in NLP should eventually go through it carefully. It describes the "meta-model" patterns for asking clients questions. The Structure of Magic, vol. 2 (1976) discusses various aspects of non-verbal communication and is no longer very popular reading. Some things in it are certainly dated. However Robert Dilts considers it one of the most important NLP books.
Patterns in the Hypnotic Techniques of Milton Erickson, vol. 1 & 2 (Meta Press, 1975, 1977) is the original Bandler-Grinder study of Milton Erickson. It is written in a fairly dry attempt at a scholarly style. The book is still essential reading (IMHO) for anyone with a serious interest in hypnosis.
NEURO-LINGUISTIC PROGRAMMING, vol. 1 by Dilts, Grinder, Bandler, DeLozier, and Cameron-Bandler (Meta Publications, 1979) represents the systems-theory side of NLP. This book is less popular than many others, but contains some fundamental ideas. (There has never been a volume 2.)
Steve and Connirae Andreas took tapes of some of the Bandler-Grinder seminars and edited them into three books called FROGS INTO PRINCES (Real People Press, 1979), Trance-Formations (1981), and Reframing (1982). These books have the excitement of the early Bandler-Grinder seminars as well as many of the faults. They represent things Bandler and Grinder said while standing in front of an appreciative seminar audience. They are full of dramatic anecdotes about Bandler and Grinder's work with various clients, along with a somewhat unsystematic but engrossing presentation of the basic ideas and techniques. They were given new age covers and published by Real People Press in Utah, and have sold large numbers of copies in mainstream bookstores across the country. Much more recently, the Andreases have edited two more books with the same format which present the NLP "submodality" techniques: Using your Brain -- for a Change (1985) by Bandler, and Change Your Mind and Keep the Change (1987) by Steve and Connirae Andreas themselves.
Heart of the Mind by Connirae and Steve Anreas (Real People Press, 1989) is probably the best place to start for someone wanting to learn what NLP is today.
Introducing Neuro-Linguistic Programming by Joseph C'Connor and John Seymour (Mandala [Harper-Collins], 1990) is a very good systematic introduction to NLP. It is much better organized and more complete than those books which are transcripts of seminars. Unfortunately, it also lacks the dramatic appeal of those books. It is intended for serious students.
Practical Magic by Steve Lankton. This is one of the earliest NLP books. It describes the oldest NLP techniques (pre-submodalities) and relates them to techniques used in other, more traditional forms of therapy.
Beliefs --- Pathways to Health & Well Being, by Robert Dilts, Tim Hallbom & Suzi Smith [Metamorphous Press, 1990] is a good general introduction to the main NLP ideas and is of special interest of those interested in applications of NLP to health.
The Core Transformation by Connirae Andreas. This came out in January, 1994. Connirae Andreas & NLP Comprehensive are extremely enthusiastic about it and are doing their best to promote it to the "mainstream audience" --- which I guess means to therapists with no NLP background. I am told that "It puts heart into NLP." (A frequent complain about NLP is that it's too mechanical, although as a student of Leslie Cameron Bandler I certainly never believed that.)
Time for a Change. This is Richard Bandler's latest book. It is more about attitude than technique and I guess should be classed as an "inspirational" book, although some will think that a strange term to apply to anything by Bandler! I think there are a lot of good things in it, but I don't think it's a good place to look to find out what NLP is.
The source I use for NLP books and tapes is NLP Comprehensive, 12567 W. Cedar Dr #102, Lakewood, CO 80228 (800) 233-1657. This was founded by Steve and Connirae Andreas and I have found them to be fast and reliable. They publish a glossy catalog of books and videotapes which is available for the asking. Just looking through this catalog will give some idea of what NLP is about.
There are many other NLP Centers around the country and I'm sure that many of them have a lot to offer. (See the file NLP Training Centers in my archive.) NLP Comprehensive happens to be the one I'm familiar with.