The other night I spent 15 or 20 minutes with Listening In, which contains selections from John F. Kennedy's White House tapes. (Didn't buy it, partly because I'm on a fairly tight budget for such things.) There is a good deal here that will interest those students of the history of U.S. foreign policy who haven't already had access to the tapes (not sure of the details, but I think the Kennedy Library has now made a lot of them available online, though perhaps the audio is not always great; with this book, however, you get transcripts, Ted Widmer's comments as editor, plus a couple of CDs).
There are, among other things, sections on nuclear weapons, Vietnam, and the Cuban missile crisis. Looking through it quickly, I was particularly struck by a phone conversation between Kennedy and Harold MacMillan in which JFK several times calls the considerably older MacMillan 'Prime Minister', while the latter, without in any way seeming to give affront, manages to avoid calling JFK 'Mr. President'.
The book has a foreword by Caroline Kennedy, who refers to her father as the "first truly modern president." There are various ways in which I think that's true (one thinks here in terms of style, the opening of the White House to artists (e.g. the Casals concert) and intellectuals that was so much a part of the Camelot aura, and the fact that JFK was the first president born in the twentieth century ("the torch has been passed to a new generation, born in this century....")). However, it was during his predecessor Eisenhower's administration that the U.S. became recognizably 'modern' in some ways that persist (e.g., the centrality of the car, the rise of the suburbs).
As Widmer points out, the tapes would have been used by Kennedy as raw material for his memoirs, had he lived to write them. The fact that he didn't makes them all the more valuable to historians and the interested public.