U.S. Navy DEVGRU (SEALs)
Formerly known as "SEAL Team Six" they are the elite Navy SEALs version of Delta Force. They are a counter terror unit that combines the abilities of units such as the SAS, SBS, and 1st SFOD-D (Delta Force).
The United States Naval Special Warfare Development Group, commonly known as DEVGRU or SEAL Team Six (ST6) by civilians, is the United States Naval Special Warfare Command's tier-one special missions and counter-terrorism unit. It is located at Dam Neck, Virginia. DEVGRU operators are selected from the current United States Navy SEAL Teams. DEVGRU it is the evolutionary descendent of super-secret SEAL Team Six which was created as part of the Joint Special Operations Command in 1980.[1]
The Development Group is active in both the Global War on Terror and the Iraq War. DEVGRU has worked closely with Delta Force and civilian government agencies in special task forces (TF) to kill or capture the leaders of terrorist organizations such as Al-Qaeda, the Taliban and insurgent groups in Iraq and Afghanistan.[11][12] One such task force known as TF 145, TF 6-26 and TF 121 have conducted controversial operations in Iraq that led to the capture of the late Saddam Hussein and the death of the leader of Al-Qaeda in Iraq Abu Musab al-Zarqawi.[12][13][14]
I also think that the CIA's paramilitary groups are amoung the top as well.
The Special Activities Division (SAD)[1] is a division of the Central Intelligence Agency's former Directorate of Operations, now the National Clandestine Service, responsible for covert paramilitary operations, effected when the U.S. Government does not wish to be overtly associated with such activities[2]. As such, members of the unit, when on missions, normally do not carry any objects or clothing (e.g., military uniforms) that would associate them with the United States. SAD has been changed to Special Services Office in recent years.
Even after creation of the National Clandestine Service, there remains tension between the NCS and the Department of Defense, over roles and missions in direct action such as raids, sabotage and assassinations, unconventional warfare (i.e., training and leading guerillas), Foreign internal defense[3] (i.e., training and sometimes leading counterguerilla forces) and deniable psychological operations, the latter also known as black propaganda. Special reconnaissance is another area that can be under either military or intelligence, as well as certain counterintelligence operations.
SAD officers are trained at Camp Peary (also known as "The Farm") in Virginia, and at privately owned training centers around the United States. According to a Time Magazine article "America's Secret Army", within the international intelligence community the SAD is considered to be one of the most skilled Special Operations forces in the world.
SAD officers have operated covertly since the mid 1970s in places such as Lebanon, Iran, Syria, Libya, Iraq, El Salvador, Guatemala, Colombia, Nicaragua, Honduras, Chile, Bosnia, Serbia, Somalia, Kosovo and Afghanistan.
The good old CBO'S (Clandestine Black Ops Soldiers) 
). 
