[Steuard]

Wholeheartedly seconded. This book occupies a nearly unique position in the physics literature: it is neither a textbook nor a popularization. It assumes little more knowledge (of math or physics) than the typical popularization, but it explains what is very nearly the true, complete structure of its subject matter (quantum electrodymanics). Now, the methods that it teaches are absolutely unwieldy: it would be hopeless to do any real, meaningful calculation by drawing countless little arrows! But (as I think Feynman says) you can go to grad school to learn the efficient tricks. The underlying concepts will carry through essentially unchanged.

I wish I could write like that.

[lobster_johnson]

An interesting and surprising fact about Feynman's books is that he never _wrote_ any of them, as such; he famously disliked writing. QED is essentially a transcript of a lecture (although I don't know how much polishing and editing was done by Feynman himself; probably some). Same with his collection of physics lectures. His most popular book, "Surely You're Joking, Mr. Feynman", was transcribed from a series of interviews, pretty much verbatim.

[furyofantares]

Relativity: The Special and General Theory by Einstein would also fit that description, I think. (Though I haven't read Feynman's book so I may be misunderstanding you.)