As a guy deeply interested in Watergate, I had to have John W. Dean's new book on this subject, The Nixon Defense. Dean listened to a lot of those White House tapes that no one else had listened to — or at least, no one who knew enough to know the significance of most of what was said about them. It's amazing that, this long after Nixon was almost impeached, we're still learning reasons why he should have been. This review by David Greenberg gives a good summary of what Dean found on those tapes.