In his Contribution to the Theory of the Trade Cycle, he introduced a Harrodian multiplier-accelerator system with ceilings and floors, and his 1937 paper "Mr. Keynes and the Classics" proposed his liquidity trap and IS-LM model.  
His article "Monopoly" proposed the concept of conjectural variations to connect various imperfect competition theories.  In his Theory of Wages, he restated the marginal productivity theory, and he introduced the Slutsky decomposition of demand into income and substitution effects.  His work in welfare economics produced his namesake compensation criteria for ordering allocations and 1956's Revision of Demand Theory.  In his Contribution to the Theory of the Trade Cycle, he introduced a Harrodian multiplier-accelerator system with ceilings and floors, and his 1937 paper "Mr. Keynes and the Classics" proposed his liquidity trap and IS-LM model.  Probably his most famous work, which laid out the conditions for stability of general equilibrium, is 1939's Value and Capital.  FTP name this economist who shared the 1972 Nobel Prize with Kenneth Arrow, also the namesake of a demand curve based solely on substitution effects.
His article "Monopoly" proposed the concept of conjectural variations to connect various imperfect competition theories.  
John Hicks