Nixon (and other presidential) tapes online
"Between 1940 and 1973, six American presidents from both political parties secretly recorded just under 5,000 hours of their meetings and telephone conversations."
That's a quote from the website of the Presidential Recordings Program of the Miller Center of Public Affairs at the University of Virginia, which provides audio clips and transcripts of the tapes for free online, plus some commentary.
The presidents in question, of course, were Roosevelt, Truman, Eisenhower, Kennedy, Johnson, and Nixon.
A fascinating resource; if I had time, I would go listen to samples and post links to specific items.