WhiteHouseTapes.org. Secret White House tapes and recordings of Presidents Kennedy, Johnson, Nixon, Roosevelt, Truman, and Eisenhower.
From the site:
Between 1940 and 1973, six American presidents from both political parties secretly recorded just under 5,000 hours of conversations. This site is designed as a service to the research community by making freely available all of the presidential recordings, along with relevant research materials, so that scholars, teachers, students, and the public can hear and use these remarkable tapes for themselves. The site is hosted and maintained by the Presidential Recordings Program at the University of Virginia's Miller Center of Public Affairs.