Speaking of which, her letters have just been published, that would be interesting. A few years ago, a fascinating sort of collective biography of the Mitford sisters came out–amazing stuff. Sort of a snapshot of the 20th century all in one family.
Another vote for O’Rourke’s A Parliament of Whores. You’ll never think of Congress the same way again.
I really enjoyed Richard Brookhiser’s Founding Father: Rediscovering George Washington, which has a gentle sense of humor but also very entertainingly explores Washington’s life and legacy. Brookhiser explains why Washington deserves a lot more respect and admiration than he gets nowadays, when he’s practically mummified in the public imagination.
Last Chance to See, by Douglas Adams (the Hitchhiker’s Guide author) and a coauthor whose name escapes me, is a very, very funny look at a profoundly unfunny topic, probably-doomed efforts to protect extremely endangered animals.
I appreciate the responses and see no shortage of enjoyable material in the coming months 
I’m currently working on ‘Metaphors We Live By’ and ‘Influence’, which are both interesting, but unfortunately completely devoid of any humor. I’ll pick off a few from this list afterwards.
Since your OP recommended the first thing I was going to say, might I add Dr. Tatiana’s Sex Advice for All of Creation by Olivia Judson - the most humorous and hottest biology book you’ll ever find.