For more see the Government Information portal at Columbia. If you are unfamiliar with how the American Government is set up (it's confusing!) please consult this fabulous set of resources from USA.gov.
U.S. Departments
Department of State: The primary source of foreign affairs information for the U.S. Government and is responsible for implementing the President's foreign policies.
Don't forget that the State Department has had many versions of their website that can be accessed at their web-archive.
Background Notes - U.S. Department of State: Brief profiles of most countries of the world. Includes information on government type and structure, names of major government officials, and an overview of foreign relations.
Department of Homeland Security: On March 1, 2003, the majority of 180,000 employees from 22 agencies were merged to create the 15th department in the federal government. The department has three primary missions: prevent terrorist attacks within the United States, reduce America's vulnerability to terrorism, and minimize the damage from potential attacks and natural disasters.
National Archives: Links and indexes to government publications in the National Archives.
Science.gov : Provide users with access to more than 200 million pages of authoritative federal science information including research and development results.
USA.gov: Official guide to government information and services
ProQuest Tools
ProQuest Congressional: This is the most comprehensive online resource available for congressional publications and legislative research.
ProQuest Legislative Insight: This is a federal legislative history service that makes available thoroughly researched compilations of digital full-text publications relevant to enacted U.S. public laws.