This list is from my lecture Monday night:
David Hume: His essay on money, circa 1752, remains one of the best writings on the topic. Honorable mention goes to Isaac Gervaise, who in 1734 outlined international mechanisms of adjustment.
Adam Smith: Growth is everything, no?
Thomas Malthus: A much underrated macroeconomist. He grasped aggregate demand, and price-cost margins, not to mention the importance of demographics.
David Ricardo: Not an original macroeconomist, but he showed you could apply the quantity theory of money to the policy issues of the day.
Henry Thornton: Super-smart, he integrated the best of all previous macroeconomics without making an error. He didn’t have much influence until Wicksell and the Austrians, however.
Knut Wicksell: He showed it was possible to have an integrated analysis of the real and monetary sectors of the economy. He also anticipated about 90 percent of modern real business cycle theory.
Milton Friedman: Many of his most important ideas were a resurrection of previous wisdom, most of all from Irving Fisher, but his practical influence has been vast.
The 1979-1990 Theory Boom: We applied every idea in the toolbox — from game theory to adverse selection to imperfect competition — to macroeconomics. But who gets the credit?
Next on the horizon: ????? When it comes to high theory, we live in slow times.
Dark horse pick: Friedrich Hayek (or is it Mises?); even Paul Krugman is borrowing his ideas.
Addendum: Wesley Clair Mitchell also deserves mention, and read the second comment below for other names.