Benjamin Graham's Intelligent Investor
Benjamin Graham (1894-1976), is credited to be the father of value investing. In this book written in 1949 was a precursor in the field. The argument he makes for value investing is rational and compelling.
This is Warren Buffet's favorite investment book. The exposition is clear and the prose well rounded.
Rather than buying stocks because their price just went up, Graham makes the point that a stock is actually a share of a company, and that being able to value the business and applying a margin of safety allows you to make an informed decision when the irrational Mr. Market (a personification high on animal spirits) is ready to sell the business for too little or to buy it for too much.
I first read this book around 2000 and despite it being written 50 years before, it had not aged at all. It is still one of the best book on the subject.
An excellent summary by the sweedish investor is available here.