The 160th Special Operations Aviation Regiment (Airborne) aka Night Stalkers or Task Force 160 and have been mentioned in a couple recent episodes of UFO Hunters on The History Channel. Besides some possible UFO connections these guys may also be responsible for many of the "black helicopter" reports out there.
Started back in 1980 after the hostage rescue failure in Iran, these guys specialize in night flying (explains the black paint jobs on their helicopters) at low altitudes. They are also trained to move in and get out quickly and were involved in some recent historical military missions, including the incident Blackhawk Down was about.
According to the Wikipedia page on these boys (the only women are staff) they fly three different helicopters and their variants, including the CH/MH-47 Chinook, MH-60 Blackhawk, and AH/MH-6 Little Bird. However besides looking good in black paint jobs, these guys may, as already mentioned, have connections to a couple UFO incidents that were covered on UFO Hunters.
The first incident is a famous and mysterious case involving 3 eye witnesses who saw a mysterious diamond shaped craft in the middle of a Texas highway. As they were watching the craft a group of large helicopters (possibly CH-47 Chinooks) surrounded the object and apparently escorted it from the area. All witnesses later began to experience what doctors could only diagnose as radiation sickness. The case is now known as the Cash-Landrum (Wikipedia and Tinwiki) incident (named after the witnesses) and is one of the most mysterious in UFO history. It's also worthy to note that this incident occured in 1980, when the Night Stalkers were first formed. Whether or not the helicopters seen where from the Night Stalkers is not known for sure.
The other incident involves a crash of a mysterious object in Needles California on March 14th, 2008. Initially it appeared it was a meteorite, but shortly after the crash not only were black military helicopters seen (retrieving the object none the less) in the area, but planes that fly people to Area 51 were present at a nearby airport in Laughlin. So not only do we have the Area 51 connection, but also black helicopters which are possibly part of Task Force 160 (as mentioned in UFO Hunters) which has a battalion based north of California in Fort Lewis Washington. Interesting if I do say so myself...wonder what they recovered...
Anyways, for those who haven't checked it out, I highly recommend catching UFO Hunters on The History Channel which is quite possibly the best UFO show out there. Also here is some reading material I dug up on the Needles Crash:
UFO Crash and Retrieval at Needles California - About.com
Did a UFO Crash in Needles California Earlier this Summer? - Alien Seeker News