I don't think I can really do this question justice. A lot of us probably have different things that come to mind when we think of the history of economics. I tend to take an academic interpretation of your question.
A potpourri of random (mostly microecon, but maybe it'd be better to sort them) events that come to mind:
1838 - Supply and Demand:
Antoine Augustin Cournot publishes a book about the supply and demand model (Alfred Marshall makes it famous later).
1870s - General Equilbirum Theory:
William Stanley Jevons, Carl Menger, and French economist Leon Walras develop around the same time the idea of marginal utility, and Walras in particular creates his work in 1874, "Elements of Pure Economics"
1915(?) - Slutsky Decomposition:
Eugen Slutsky relates Marshallian and Hicksian demand to separate income and substitution effects. In 1927, he did something with statistics and business cycles that I don't quite understand, but I think that was important too.
1930 - Intertemporal Consumption:
Irving Fisher lays out early work on discounted saving, though arguably, Modigliani & Brumberg (1954), Albert Ando, and Milton Friedman (1957) and the work on the life cycle-model is more noteworthy.
1944 - Game Theory:
John von Neumann and Oskar Morgenstern use Brouwer's fixed-point theorem to create the basis for game theory.
1947 - Von-Neumann Morgenstern Utility
John von Neumann and Oskar Morgenstern create their four axioms surrounding rationality with probabilistic utility outcomes.
1951 - Arrow's Impossibility Theorem:
Joseph Kenneth Arrow publishes his book, "Social Choice and Individual Values"
1973 - Black-Scholes Pricing Model:
1977(?) - Mechanism Design:
Leonid Hurwicz, Eric Maskin, and Roger Myerson create the foundation for "reverse game theory".
As you can see, there are lots of gaps. I still don't know a lot about economic history--just that it is very large.
Other topics to add: Behavioral economics, experimental economics, information economics
