Last month over 60 declassified documents were posted on the internet by the National Security Archive. It does look like, however, not much has been released on any alien or UFO activities.
A large number of the declassified documents focus on the governments quest to develop stealth aircraft, and the exploitation of covertly acquired soviet MiG fighter jets.
On of the documents dating from April 1962, discusses the logic behind photographing Area 51 by means of high flying plane or by a CORONA satellite, which also was classified at the time. The reasoning behind this was to try determine how much the Soviet Union could learn from spying on the location.
Head over to LiveScience here for more details from the reports.
To access the archive directly, head over to the National Security Archive site here.