Federal Government of the United States

American FactFinder from U.S. Census Bureau
Source for population, housing, economic, and geographic data including American Community Surveys.

Ben's Guide to the U.S. Government For Kids
Fantastic site for kids 3rd to 5th grade. Covers topics including as law, governmental branches, citizenship, and federal vs state government.

FirstGov.gov
The U.S. Government’s official Web portal providing links to government information at all levels of government by topic and by organization.

Library of Congress
Includes the US Copyright Office, and many other resources

Project Vote Smart
Tracks the performance of more than 40,000 office holders and candidates for public office. Resources include voting records, issues information, background information, campaign finances and performance evaluations made by over 100 liberal to conservative special interest groups, and other directories of political information. A great feature is the ability to type in your zip code and get back information on all your representatives, state and federal, including biographical, address, committee assignments, etc. An excellent resource.

THOMAS: Legislative Information on the Internet
Databases providing access to the full texts of bills and laws from the United States Congress, the daily Congressional Record, relevant proceedings and proposed legislation, committee reports, and roll call votes, variously available from the present back to the 93rd Congress (1973). The site includes links to major U.S. legislative Web sites.