The Documents Center website of the University of Michigan contains extensive information about the federal government, and its Judicial, Legislative, the Executive branches. Also included are foreign government information sources, federal statistics, and other government-related topics.
FedWorld.gov
FedWorld.gov is "a gateway to government information." This site is maintained by the National Technical Information Service (NTIS), of the US Department of Commerce, and serves as the online locator service for a comprehensive inventory of information disseminated by the Federal Government.
The United States Government Manual
The U.S. Government Manual is the official handbook of the Federal Government and provides comprehensive information on the agencies of the legislative, judicial, and executive branches.
USA.gov
The official U.S. gateway to all government information; it offers access to thousands of government websites from a single central point. Sites are categorized by topic. Those looking for a specific department or agency can browse hierarchical listings of the three branches of government located on the left-hand column of the homepage.