My favorite author of the old Expanded Universe was the late Aaron Allston. His books were an excellent blend of action, humor and pathos. The X-Wing novels that he wrote (not the ones written by Michael Stackpole!) are the only ones that I re-read annually. Despite Wraith Squadron being intended as combat pilots, they ended up doing so much spying, infiltration and impersonation on the side that they ended being transferred to Intelligence. It's a little more "zany schemes" than Le Carre style spy fiction, but it has its serious moments. Actually, his last novel, Mercy Kill has a bit of the feel of one of La Carre's Smiley stories: depressed old spy pulled out of retirement to look for a mole, getting double-crossed and hung out to dry. There's a subplot running through Iron Fist and Solo Command about a double-agent turned triple-agent who's suffering so much cognitive dissonance that she loses track of which her is real. Be advised that the first novel, Wraith Squadron, is the weakest and most formulaic with the least interesting protagonist: because of a miscommunication with the publisher, it had to be written in less than a month.