[NOTE:  Prompted by Cho, this is a very basic toolbox including links to some legal websites.]

This is designed to be added to, so please add sites and/or topic headings (legal, or with a legal focus).  Thanks.  Enjoy.

Basics:

Constitution of the United States [Annotated]

-  U.S. Constitution.  Lists Articles & Amendments with annotations, as well as The Constitution of the United States of America: Analyis and Interpretation by the Congressional Research Service, Library of Congress. [1992, '96, '98, Y2k Supplement].

U.S. Government Meta-Site

-  FirstGov.  All things federal with links to all three branches, searchable.

Congress

-  Thomas.  Congressional information, including cong. record, appointees, committees, Public Laws.  Information for/by each house available through this site.

Overview of the American Judicial System

-  Understanding U.S. Courts from the U.S. Courts website.  Quick and informative background read, including this map [.pdf].