Things I didn't know about Nixon until finishing Ambrose's third volume of his biography:

--Nixon sold his New York townhouse in 1981 to the Syrian ambassador's office of the United Nations. A company involved with this arm of the UN was involved in selling uniforms to Romania, and uniforms and helicopters to Sadaam Hussein. Nixon may or may not have profited on these sales; as of 1991, Ambrose couldn't be sure.
--Nixon gave two speeches as per his resignation: one was on August 8, 1974, where he formally announced his resignation (without admitting any specific wrongdoing on his part), and one on August 9, to his family and staff, where he made his famous "deepest, darkest valley" comment. Apparently, his family and not a little of his staff was pissed that he'd arranged for the entire thing to be broadcast; in the speech itself, Nixon claimed the whole thing was not set up in advance.
--Oliver Stone must have used Ambrose's work more extensively than I thought. Of course, I suppose he could have gotten some of the dialogue directly from the tapes themselves ("Like the Germans...shoot[ing] down one villager until the rest talk" (sic)..."I really think that's what we're going to have to do..."), but other lines are from Ambrose's own observations: "Eight words back in 1972: 'I covered up. It was wrong. I'm sorry.'" Stone takes Ambrose's sentence and changes it to "I was wrong" and then delivers the line to Haldemann (played by James Woods).
--Gerald Ford pardoned Nixon more out of concern for his own administration and political future than out of worries about tearing the nation apart. I guess I should have figured that out on my own.
--Nixon spent time in W.C. Fields' former Bel Air home at a party. I think it might have been the same house Fields fell down a flight of stairs without spilling any of his drink (as per Carlotta Montijo's autobiography, admittedly problematic).

There's other stuff, but it escapes me at the moment. Volume three sticks in my head better than the others, probably because the last 100 pages covers 17 years and as a result can't be as in-depth; probably because this was the volume I was waiting for all along, with all the Watergage dirt and the resignation itself.