Anything by Garry Wills. The following books stand out, but he’s an amazingly consistent writer:
A Necessary Evil
Lincoln at Gettysburg
John Wayne’s America
Nixon Agonistes
Reagan’s America
Under God
Confessions of a Conservative
And there’s a lot of his stuff that I haven’t got around to reading yet. I think he’s the best writer on American politics and culture alive (heck, maybe the best, period), and although he’s hardly unknown (he’s one of The New York Review of Books’s main writers), he’s still underrated.
Bill Bryson’s books are great too, as is Joe Queenan, although what I read them for is style more than content.
Martin Gardner has published a slew of great books. Has anybody else read his novel The Flight of Peter Fromm?
Of course, all of Cecil Adams’s books. All of Jan Harold Brunvand’s books.
Danny Peary’s books on cult movies.
I agree with the other people who mentioned Lies My Teacher Taught Me by James W. Loewen, The Structure of Scientific Revolutions by Thomas Kuhn, and The Mismeasure of Man by Stephen Jay Gould.
It’s been decades since I’ve read it, but I recall The Music of the Spheres by Guy Murchie as being the best piece of science writing that I’ve ever read.
A couple of books that appeal to me mostly because I already know the field: The Linguistics Wars by Randy Allen Harris and Western Linguistics: An Historical Introduction by Pieter A. M. Seuren. The first is a history of the battle between two schools of generative grammar in the '60’s and '70’s. It’s not perhaps an absolute gem of writing, but it’s the best explanation of what was going on in linguistics during that period. The second is a general history of linguistics, and it is a wonderfully well-written book. For those of you who think that Noam Chomsky is a great guy, read Harris’s discussion and, more importantly, Seuren’s discussion of what an academic dirty fighter Chomsky was. His lousy argumentation and political infighting have screwed up the field of linguistics for the past couple decades.
And there’s some older writers’ stuff who I like. C. S. Lewis is great. Just to name one of his obscure books, has anybody else read Studies in Words? Does anybody else like G. K. Chesterton’s essays? Even when he gets his facts wrong, he makes interesting observations. I think that about two-thirds of Isaac Asimov’s essays are great too.