Originally Posted by SlowRain
Definitely give John le Carré a try, he's the Grandmaster of Espionage. His novels are more literary than action, though. His early stuff is a little shaky as he hadn't found his voice until the mid-1970s. He was at his peak starting with Tinker, Tailor, Soldier, Spy in 1974 and on until the late 1980s with The Russia House in 1989. Anything you choose from that time period will be brilliant. Be warned: The Honourable Schoolboy and Smiley's People are sequels to Tinker, Tailor, Soldier, Spy, so there are some spoilers--read them in order. He's been pretty good since the end of the Cold War, but the Cold War was his forte. Of his post-Cold War novels, The Night Manager, Our Game, The Tailor of Panama, and The Mission Song are pretty decent.
Also give Alan Furst a try. He writes about espionage during World War 2. He's a very spare writer, but his atmosphere alone launches him into the realms of Literature. He's very, very good.
If you can track down a copy, also try The Turn-around by Vladimir Volkoff. It's out of print now, but hopefully some enterprising e-book publisher will resurrect it. It's the only other espionage novel I've read that even comes close to le Carré in terms of narrative, character, and themes, and I've read Trevanian, Len Deighton, Eric Ambler, Adam Hall, Daniel Silva, and Tom Clancy.
Graham Greene wrote The Quiet American (very good) and The Human Factor (good). While dealing less with espionage, The Honourary Consul and The Comedians were good as well. I'm not much of a fan of his other thrillers, but you can give them a try. I think they are very similar to Eric Ambler's.
Thanks for the tip. There are so many spy novelists out there, it's hard to choose which one to start off with. I'll give LeCarre a try with the ones you pointed out. Thanks for talking about voice, that's an important detail a reader should know.