A History of the Lunar Orbiter Program: The NASA History Office offers a detailed history of the program startup, technical background, spacecraft manufacture, and mission summaries.
Lunar Orbiter: Detailed information, experiments, data, and images on the five survey missions (1966-1967).
Lunar Orbiter Photographic Atlas of the Moon: Digital edition of Lunar Orbiter Photographic Atlas, 1971, with all 675 plates.
Lunar Orbiter Program: Overviews of the various Lunar Orbiter missions, with photographs and related links.
Lunar Orbiter to the Moon: Information and data on the five lunar orbiter missions (1966-1967).
Wikipedia: Lunar Orbiter program: An overview of the five unmanned Lunar orbiter missions launched by the United States in 1966 through 1967.