The Avalon Project at Yale University has a large number of Constitutional history and many other documents, a superb collection. The site is equipped with search engines to investigate document contents. For example, a student can search the entire Federalist Papers section topic by topic. Inaugural address of the Presidents can be found at the Bartleby Project at Columbia University. From there follow directions to any of 350 cases, arranged by name of case, justice, etc.
Links also exist from there to many other constitutional and legal information sites.
Another good site for legal issues is the Oklahoma University Law School . For documents relating to the U.S. Constitution , the Constitution Society site has various documents. It also has a distinct point of view which you may find interesting. Historynet has many links to history documents and other sites of all kinds. In the Netherlands, The University of Groningen is developing a collection of documents in American history which you might like to sample.