Which is the best field guide I can buy?

• Mushrooms Demystified by David Arora is the most comprehensive single book for identifying mushrooms. It has excellent keys, descriptions, photographs, and writing. It is written primarily with the west coast of the United States in mind (although species not found in that area are covered). Less than 10% of the species covered are represented in color photographs. Mushrooms Demystified covers over 2000 species which is more than any other book you would probably consider purchasing. This book focuses on western species but still is very useful on the east coast. This is by far the best book available for west coast hunters.
• http://mushroomexpert.com - Nothing to buy here, but this site has keys that will help you identify almost any mushroom in North America.   Unfortunately it does not contain any psychoactive species.  It is more up to date than most books.
• National Audubon Society Field Guide to North American Mushrooms by Gary A. Lincoff is a good book for those who prefer to identify mushrooms by comparing collected specimens to photographs first.  Written primarily with the east coast of the United States in mind. Its greatest fault is a lack of keys.
• Dorling Kindersley/Smithsonian/Eyewitness Handbooks: Mushrooms by Thomas Laessoe, Gary Lincoff and Neil Fletcher - Not really a field  guide. Focuses primarily on European species.
• Collins Complete British Mushrooms and Toadstools: The Essential Photograph Guide to Britain's Fungi - by Barry Hughes and Paul Sterry
• Mushrooms of Northeast North America, Midwest to New England - By George Barron
• Mushrooms of North America - By Orson K. Miller Jr.
• Mushrooms of the Southeastern United States
• Mushrooms of the Midwest - By Kuo & Methven
• Edible Wild Mushrooms of Illinois and Adjacent States - By Joe McFarland and Gregory Mueller
• Mushrooms of the Upper Midwest - By Teresa Marrone and Kathy Yerich - A new book, published in the spring of 2014
• Mushrooms of West Virginia and the Central Appalachians
• Mushrooms and Other Fungi of the Midcontinental United States, 2nd Ed. -  By Huffman, Tiffany, Knaphus, and Healy
• Mushrooms and Other Fungi of North America by Roger Phillips is similar to the Audubon Guide but larger, both in size and number of species. It also has no keys for identification.
• Mushrooms by Roger Phillips is similar to the above book but centered around UK mushrooms with some European species also. Excellent presentation.
• Mushrooms of North eastern North America by Alan E. Bessette, Arleen R. Bessette and David W. Fischer is an excellent book, but limited in region to the area from North Carolina west to Kansas and north to Hudson Bay. It has excellent keys,and the photography is some of the best. Less than half of the species are represented in photographs.    For the North East USA, the website mycoquebec is better than any book.
• How to Identify Mushrooms to Genus III: Microscopic features by David L. Largent is like a user's manual for your microscope that focuses on how to use a scope to identify mushrooms. It is written for intermediate to advanced readers and has a lot of information on how to prepare samples and exactly what to look for that is difficult to obtain from any other source.
• How to Identify Mushrooms to Genus VI: Modern Genera by T.J. Baroni and David L. Largent Describes all the modern genera and has keys that use macroscopic and microscopic features to place any mushroom in its proper genus. Has great descriptions of exactly what features define the various genera and an excellent mycology glossary.  A bit outdated.
  
• Psilocybin Mushrooms of the World by Paul Stamets - A good overview of the various psychoactive species.   

A good selection of hunting books can be found at https://www.shroomery.org/books.