Open government is a belief that government is accountable to the people it serves and therefore its workings should be transparent and its document made available to the public. The Freedom of Information Act (FOIA) is a law intended to further government transparency and accountability but it is not the only mechanism to advance open government.
Open the Government is a coalition focused on policies to create a more responsive government; its site does include news related to FOIA.
Open Government Overview (U.S. General Services Administration) features initiatives focused on opening the activities of federal activities to the public.
"Report of the Office of the Secretary of Defense Vietnam Task Force" was commissioned by McNamara in 1967 and completed in 1969. The complete report has been released and serves as a history of the Vietnam War.
CIA materials (intelligence assessments etc.) related to US-Soviet relations (1980s) and provided to President Reagan and top members of his national security team.
Documents pertaining to FBI investigations of a 1985 bomb threat again Apple and a background investigation of Jobs for an appointed position on the U.S. President's Export Council.
A list of important or impactful cases before the US Supreme Court interpreting the FOIA, with accompanying opinion, information about how the justices voted and commentary.
The FOIA Wiki is still in beta format, and some sections are incomplete. It's a project of the Reporters Committee for Freedom of the Press and draws information from multiple sources.