Services/Reference works:

1. Thomas
2. U.S. Code Federal Laws
3. Federal Register
4. Code of Federal Regulations
5. What time is it? - Naval Observatory Master Clock
6. FTC Do Not Call Registry
7. NARA Archival Databases
8. Tropical Prediction Center
9. Geo. Washington Univ.'s National Security Archive
10. Near-Real-Time Earthquake List

Departments and such:

1. Dept of Health and Human Services
   • Child Support Enforcement
   • Centers for Disease Control / MMWR
   • Medwatch
2. US Postal Service / ZIP+4 Lookup
3. The President's Cabinet
4. Independent Federal Agencies and Commissions
5. FirstGov
6. FDIC
7. National Infrastructure Protection Center

Congress

1. The U.S. Senate
2. The U.S. House of Representatives
3. Library of Congress (LOC)
4. Government Printing Office (GPO)

US Government miscellany

1. Federal Budget Simulator
2. The Federal Judicial Center (FJC)
3. Commission on International Religious Freedom
4. Regulations.gov (comment on proposed regulations)