1. Albert Wohlstetter, "The Delicate Balance of Terror." Foreign Affairs (1957) Even more than Bernard Brodie or Tom Schelling, Wohlstetter laid out the basic requirements for stable nuclear deterrence. For that I can forgive him a lot of his other "contributions."
2. Mancur Olson and Richard Zeckhauser, "An Economic Theory of Alliances." Review of Economics and Statistics, (1966). This article identified and solved an intriguing puzzle, spawned an enormous literature, and still shapes how we think about alliance dynamics.
3. Kenneth Waltz, "International Structure, National Force, and the Balance of World Power," Journal of International Affairs, (1967). Clear and brief statement of Waltz’s views on bipolarity, anticipating his landmark 1975 essay in the Handbook of Political Science and the subsequent Theory of International Politics. (And I always liked it more than the earlier 1964 essay on "The Stability of a Bipolar World.")
4. Robert Jervis, "Hypotheses on Misperception," World Politics (1968). Succinct summary of how psychological tendencies can lead to erroneous judgments and poor decisions. Still worth reading today, especially if you don’t have time for the 1976 book.
5. Michael Doyle, "Kant, Liberal Legacies, and Foreign Affairs," Philosophy and Public Affairs, (1983) or "Liberalism and World Politics," American Political Science Review (1986). These articles launched the whole “democratic peace theory” debate. Others carried on this discussion, but Doyle deserves the credit for igniting the discussion.
6. John Ruggie, "International Regimes, Transactions, and Change: Embedded Liberalism in the Postwar Economic Order," International Organization (1983).
Robert Gilpin once told me he thought this was the single best article ever written in the field of modern political economy. 'Nuff said.
7. Alexander Wendt, "Anarchy is What States Make of It," International Organization (1992). The portrayal of the "Gorbachev revolution" now seems quaint, but this article did more to bring constructivist theory into the mainstream of IR than any other publication, and the theoretical arguments must be confronted.
8. Martha Finnemore and Kathryn Sikkink, "International Norm Dynamics and Political Change," International Organization (1998). The best article I've ever found for teaching students about how international norms emerge and spread, and why they are important.
9. William C. Wohlforth, "The Stability of a Unipolar World." International Security (1999). I've always wished I'd written this myself, but Wohlforth got there first and did it better than I would have.
10. Alexander George's "Case Studies and Theory Development: The Method of Structured, Focused Comparison," in P.G. Lauren, Diplomacy: New Approaches. A methodological article that guided countless Ph.D. dissertations and did more than any other single piece to trigger renewed interest in the development of rigorous qualitative methods.
Honorable Mentions: My list here could go on forever, but here are few articles that I've particularly enjoyed and/or learned from: George Kennan, "The Sources of Soviet Conduct," Foreign Affairs; Stephen Krasner, "State Power and the Structure of International Trade”, World Politics; Chaim Kauffman and Robert Pape, "Explaining Costly Moral Action: Britain and the Abolition of the Slave Trade," International Organization; Barry Posen, "Command of the Commons: The Military Foundation of U.S. Hegemony, International Security; James Fearon, "Rationalist Theories of War," International Organization; Andrew Mack, "Why Big Powers Lose Small Wars: The Politics of Asymmetric Conflict,” World Politics; Robert Jervis, "Cooperation under the Security Dilemma, World Politics; and "Why Nuclear Superiority Doesn't Matter," Political Science Quarterly; Robert Keohane, "The Demand for International Regimes," International Organization; John Gaddis, “The Long Peace: Elements of Stability in the Postwar International System,” International Security; Stanley Hoffmann, "Obstinate or Obsolete: The Fate of the Nation State in Western Europe," Daedalus; Timur Kuran, “Now out of Never: The Element of Surprise in the Revolutions of 1989," World Politics; and Graham Allison, "Conceptual Models and the Cuban Missile Crisis," American Political Science Review.