Milton Friedman? There’s a lot. His most influential academic books are probably A Theory of the Consumption Function, A Monetary History of the United States (coauthored with Anna Schwartz), and maybe Essays in Positive Economics. For general audiences, there’s Free to Choose, Capitalism and Freedom, and his columns for Newsweek, among much else. There’s a pretty good short book on Friedman’s work written by Steven Landsburg, titled The Essential Milton Friedman.