The Avalon Project at the YaleLawSchool has a feature entitled The American Constitution - A Documentary Record that includes texts of many documents relating to the development of the Constitution. An annotated text of the Constitution is available through Congresslink. The following sections of the U.S. Constitution are especially relevant:
---Article I Legislative Branch Section 1, 2, 3, 7, 8
---Article II The Executive Branch Section 1, 2, 3
---Article III The Judicial Branch Section 1, 2
---Congresslink also features 10 Things Every Student Should Know About Congress
Building Freedom, Building Security: Building Checks and Balances for National Security Policy: The Role of Congress
Suggested recent topics: Constitution and Checks and Balances, Line-Item Veto, Impeachment, Patriot Act, Direct Democracy, Military Tribunal, Habeas Corpus.