Summarizing Becker’s contributions is like trying to summarize economics and it is not really possible. I believe he has the best “30th best” paper of any economist, living or dead.
Here are a few Becker articles which are not even his best known work:
1. “Irrational Behavior and Economic Theory.” Can the theorems of economics survive the assumption of irrational behavior? (hint: yes)
2. “Altruism, Egoism, and Genetic Fitness: Economics and Sociobiology.” The title says it all, from 1976.
3. “A Note on Restaurant Pricing and Other Examples of Social Influence on Price.” Why don’t successful restaurants just raise the prices for Saturday night seatings?
4. “The Quantity and Quality of Life and the Evolution of World Inequality” (with Philipson and Soares). The causes and importance of converging lifespans.
5. “Competition and Democracy.” From 1958, but most people still ignore this basic point about why government very often does not improve on market outcomes.
6. “The Challenge of Immigration: A Radical Solution.” Auction off the right to enter this country.