This is for mechanical/system traders ... What one book turned the tide for you and led/helped you develop profitable systems? Feel free to PM me if you don't want to post this to the world. (those who don't like/believe in books or systems, go right onto the next thread
Good God Almighty, there are a lot more than one. My own personal top TWO, that led me to the greatest number of profitable fully-mechanical systems for futures trading, are LeBeau and Lucas, Computer Analysis of the Futures Markets, http://www.amazon.com/exec/obidos/tg/detail/-/1556234686/ Kestner, Quantitative Trading Strategies, http://www.amazon.com/exec/obidos/ASIN/0071412395/
Van K Tharp "trade your way to financial freedom" = helped me step away from the masses mentality and develop my own price based system. LeFevre(Livermore) "Reminiscences of a Stock Operator" = Enabled me to look past day to day fluctuations and embrace the big picture. IMO the best 2 books on the subject of trading.
http://www.amazon.com/exec/obidos/tg/detail/-/0471027294/103-4370336-0949406 I purchased this book too early in my trading career (while I was still looking for "the grail" in one place). It's one of the very few that I would replace if all my trading books were lost to a natural disaster.