Notorious (the Cary Grant/Ingrid Bergman/Claude Rains/Hitchcock one, not the recent dreck with the same title)
http://www.imdb.com/title/tt0041959/
....You'd be hard pressed to find a movie that better combines espionage and suspense, ever. Add to that some real relationship chemistry and a subplot of redemption- and you get one of the finest movies ever made.
The Third Man
A man shows up in post war Vienna to accept an old friend's job offer...but finds not only that his friend is dead, but that he's assumed to have been an underworld figure. No one's that interested in investigating the death, and when the man finds that there was an unknown "third man" on the scene, he starts investigating on his own. Orson Wells in his pre-whale days does a bang up job writing, acting, and directing in this one.
Touch of Evil 
Charlton Heston plays a respected Mexican official who's investigating corruption that crosses to the north of the border, and whose wife (Janet Leigh of Psycho fame) gets kidnapped for his trouble. Orson Welles plays the very large sherriff from the US side. Landmark movie as it's generally considered the last of the true Film Noir school, and one of the very best of them all. Also impressed by the fact that the movie both treats the Mexican character as a straight up protagonist, and that he was married to a beautiful caucasian woman. Really radically aggressive moves in the 50s!
