link to original reddit post by /u/HighlandValley
LOTS of options... (incomplete list)
ACF - Administration for Children and Families
AHRQ - Agency for Healthcare Research and Quality
AMS - Agricultural Marketing Service
APHIS - Animal and Plant Health Inspection Service
ATF - Bureau of Alcohol, Tobacco, Firearms, and Explosives
BEA - Bureau of Economic Analysis
BEP - Bureau of Engraving and Printing
BIS - Bureau of Industry and Security
BLM - Bureau of Land Management
BOP - Bureau of Prisons
BSEE - Bureau of Safety and Environmental Enforcement
CBO - Congressional Budget Office
CDC - Center for Disease Control and Prevention
CENTCOM - Central Command
CFTC - Commodity Futures Trading Commission
CIA - Central Intelligence Agency
CISA - Cybersecurity and Infrastructure Security Agency
CMS - Centers for Medicare and Medicaid Services
CNPP - Center for Nutrition Policy and Promotion
COPS - Community Oriented Policing Services
CPIR - Center for Parent Information and Resources
CPSC - Consumer Product Safety Commission
DARPA - Defense Advanced Research Projects Agency
DEA - Drug Enforcement Agency
DFAS - Defense Finance and Accounting Service
DHS - Department of Homeland Security
DIA - Defense Intelligence Agency
DISA - Defense Information Systems Agency
DLA - Defense Logistics Agency
DOC - Department of Commerce
DOD - Department of Defense
DOE - Department of Energy
DOI - Department of the Interior
DOJ - Department of Justice
DOL - Department of Labor
DOS - Department of State
DOT - Department of Transportation
DSCA - Defense Security Cooperation Agency
DTIC - Defense Technical Information Center
DTRA - Defense Threat Reduction Agency
ED - Department of Education
FAA - Federal Aviation Administration
FBI - Federal Bureau of Investigation
FCC - Federal Communications Commission
FDA - Food and Drug Administration
FDIC - Federal Deposit Insurance Corporation
FHA - Federal Highway Administration
FTA - Federal Transit Administration
FTC - Federal Trade Commission
FWS - Fish and Wildlife Service
FEMA - Federal Emergency Management Agency
FRA - Federal Railroad Administration
HHS - Department of Health and Human Services
HUD - Department of Housing and Urban Development
ICE - Immigration and Customs Enforcement
NARA - National Archives and Records Administration
NASA - National Aeronautics and Space Administration
NEA - National Endowment for the Arts
NFIP - National Flood Insurance Program
NHIC - National Health Information Center
NHTSA - National Highway Traffic Safety Administration
NLRB - National Labor Relations Board
NIDCD - National Institute of Deafness and Other Communication Disorders
NIDDK - National Institute of Diabetes and Digestive and Kidney Diseases
NIFA - National Institute of Food and Agriculture
NIH - National Institute of Health
NIST - National Institute of Standards and Technology
NOAA - National Oceanic and Atmospheric Administration
NPS - National Park Service
NSA - National Security Agency
OCC - Office of Comptroller of the Currency
OCSE - Office of Child Support Enforcement
ODEP - Office of Disability Employment Policy
TSA - Transportation Security Administration
USAID - Agency for International Development
USCIS - Citizenship and Immigration Services
USDA - Agricultural Department
US CERT - Computer Emergency Readiness Team
VA - Department of Veterans Affairs
That's all I can muster up the energy to type. FYI - only about half of federal agencies/departments have an initialization. Missing from the above list and without initials are things like the Dept of the Treasury, Fannie Mae, Federal Reserve System, etc.