The Poor Bloody Infantry 1939-1945, Charles Whiting, Arrow Books, 1989
This is just a must have. A book that deals with the men who fought the battles,  particularly the infantry. And although it mainly deals with the British, it also covers other nations. The theme is to uncover the man, his motivations, conditions, morale, and how he was often sacrificed. It is moving and revealing of the spirit of men as they are slowly crushed in the war about them. Wargamers of any period could learn from how his troops might really feel as he commands them.

Commando Extraordinary, Chales Foley,    Pan Books, 1956,1957,1970,1974
The true and full story of Otto Skorzeny as told to the writer by Otto himself. It shows the man and his exploits, not the myths and legends which seem to follow him. Once described as the most dangerous man in Europe, his legend was greater than the man himself, but not by much. A preacher of the unorthodox and unconventional, he even gives an opinion on future conflict and special operations. This book is well worth hunting down.

Ultra Goes To War- The secret story, Ronald Lewin, Anchor Press Ltd., 1978
This might not strictly be a wargamers book, but I think having read it you will change you mind. If you have read 'The Ultra Secret' or 'Code Breakers- The inside Story of Bletchley Park' you will be familiar with a lot of this. It is the story of the code breaking of the German Enigma ciphers before and during WW2. Now what makes this interesting is how the information was used by the commanders and  Generals to conduct the war, plan operations, and even vital low level intelligence of the enemy in front of you. As with 'The Ultra Secret', it is interesting to note how the various commanders use the information. For example the myth of 'Monty' being a great commander comes into doubt, as does a number of other generals, and how the politicians used the information and interfered with military matters. If nothing else this book demonstrates the importance of intelligence, received in time, and            accurately interpreted.