I recently finished reading through Tinker, Tailor, Soldier, Spy. I hadn't read a spy/espionage book since early high school, when I blitzed through every Tom Clancy book ever, then got burned out on them and turned to beat poetry.
In Tinker, Tailor Le Carre fulfilled my desire for espionage topics with my desire for skillful writing. This book completely engrossed me. It was so different from other spy/action books that I had read because it focused so much on the mental and moral side of things, instead of the physical and action oriented side. Indeed, the only action that happens in Tinker, Tailor is told in a flashback at the end.
The next chance I get I'm definitely going back to McClure's (they had a whole Le Carre section) to get The Honorable Schoolboy and Smiley's People, as well as some others. Wonderful writing.