Even though I devoured Ian Fleming's Bond books, I never was much for spy novels. I'm discovering them now with great delight. Naturally, I have my preferences - I haven't read a Bourne novel but I don't think I would like them. No, Ashenden showed me the way. Then I tracked down Eric Ambler. Rediscovered LeCarre - have since read the amazing Tailor, Tinker, Soldier, Spy. Richard Condon's Manchurian Candidate blew me away. Now am hip deep in The Miernik Dossier and loving it.
Next - Len Deighton? Everything I need to know to get started is here.