US Government Agencies: Blacklist compiled by SquidBlacklist.org on 3/17/2013.
DEPARTMENT OF DEFENSE, SUPREME COURT, CONGRESS, US MILITARY, LAW ENFORCEMENT, CIA, FBI, DHS, DEA, ATF, FEMA, NASA, EPA, NSA, US AIRFORCE, US ARMY, US NAVY, NATO, CDC, CONTRACTORS, PENTAGON, US MARSHALLS, SAVVIS and others…
No other public source has published a more thorough list of US Government ip ranges
http://squidblacklist.org/downloads/squidblacklists/squid-usg.tar.gz
Enjoy.