Findlaw.com - Annotated Constitution + Amendments

Interactive Constitution website w/ explanations

Constitution.org- Key constitutional issues, often comes from very reputable sources.

Important Constitutional issues with caselaw references (esp. for Units 3,4,5)

Excellent for 1st Amendment issues

The Rutherford Institute - dedicated to the defense of civil liberties and human rights

Civil Rights Project @ Harvard - Civil Rights issues

A college class website with good references to constitutional issues and cases

USconstitution.net - Notes and historical stuff about the Constitution