An updated list, with Duck Soup taking pride of place at the top. Because it is a comedy and generally regarded as a satirical war film, I'd forgotten it is principally a film about espionage, with Chicolini and Pinky sent to spy on Rufus T. Firefly as tensions escalate between Freedonia and Sylvania.
- Duck Soup*
- North by Northwest
- The Third Man
- Notorious (1946)
- Possession*
- Nikita*
- The Conversation*
- Inception*
- The Bourne Ultimatum
- The 39 Steps (1935)
Just missing out:
Ronin*; The Ipcress File; Austin Powers: International Man of Mystery; Marathon Man*; The Lives of Others; The Manchurian Candidate (1962); Bridge of Spies; Topaz; Patriot Games; Infernal Affairs; The Man Who Knew Too Much (1956); The Departed; Tinker Tailor Soldier Spy; The Bourne Supremacy; The Bourne Identity; Zero Dark Thirty*; Foreign Correspondent
*Indicates films which are not typical 'spy films' that are ones in which at least one of the principal characters engages in espionage.