Federal Politics:

White House
Official U.S. Info.
House of Representatives
Republican National Committee
Democratic National Committee

Key Links:

About the U.S. - good for research!
(US Information Agency)
Federal Courts
(including Supreme Court)
(government documents)
Vote Smart - good for research!
(details on politicians)
Canada & other nations
(more government)

Major Agencies:

ATF (Bur. of Alcohol, Tobacco & Firearms)
BOP (Bureau of Prisons)
CBO (Congressional Budget Office)
CDC (Centers for Disease Control)
CIA (Central Intelligence Agency)
CPSC (Consumer Product Safety Comm.)
DEA (Drug Enforcement Administration)
EEOC (Equal Employment Oppty. Comm.)
EPA (Environmental Protection Agency)
FAA (Federal Aviation Administration)
FBI (Federal Bureau of Investigation)
FCC (Federal Communications Commission)
FCA (Farm Credit Administration)
FDA (Food & Drug Administration)
FDIC (Federal Deposit Insurance Corp.)
FEC (Federal Election Commission)
FEMA (Fed. Emergency Management Ag.)
FHWA (Federal Highway Administration)
FRB (Federal Reserve Board)
FTC (Federal Trade Commission)
GAO (General Accounting Office)
GPO (Government Printing Office)
GSA (General Services Administration)
HCFA (Health Care Financing Admin.)
INS (Immigration & Naturalization Service)
IRS (Internal Revenue Service)

Federal Departments:

(Census, ITA, NOAA-weather, Technology, PTO)
Defense (Army, Navy, Air Force, Marines)
Health & Human Services
(CDC, FDA, HCFA-medicare/aid, NIH)
Housing & Urban Development
(DEA, FBI, INS, BOP, US Marshals)
State (travel & consular info)
(Coast Guard, FAA, FHWA, NHTSA-crash tests)
(ATF, Customs, IRS, Mint, Secret Service)
Veterans Affairs

ITA (International Trade Administration)
LOC (Library of Congress)
NARA (Ntl. Archives & Records Admin.)
NASA (Ntl. Aeronautics & Space Admin.)
NEA (National Endowment for the Arts)
NEH (Ntl. Endowment for the Humanities)
NHTSA (Ntl. Highway Traffic Safety Admin.)
NIH (National Institutes of Health)
NOAA (Ntl. Oceanic & Atmospheric Admin.)
NRC (Nuclear Regulatory Commission)
NSF (National Science Foundation)
NSA (National Security Agency)
NTSB (Ntl. Transportation Safety Board)
OPM (Office of Personnel Management)
PC (Peace Corps)
SEC (Securities & Exchange Comm.)
SBA (Small Business Administration)
SI (Smithsonian Institution)
SSA (Social Security Administration)
USAID (US Agency for Intl. Development)
USGS (US Geological Survey)
USIA (US Information Agency)
USOGE (US Office of Government Ethics)
USPS (United States Postal Service)
USPTO (US Patent & Trademark Office)
VOA (Voice of America)