I could easily make a top 10 from the lists already posted. I'll only repeat a couple. Thanks to Laz and Lance for their Ford picks, what a decade for him. I'll mention a less well known one, maybe not as good as the Westerns, but deserves a nod. And the Disney love from GAF and Ashley is awesome. Disney animation as a kid was a huge treat whenever it popped up. I shouldn't mention titles, but whatever. I don't know many foreign films, but Gump had Bicycle Thief. That film is heartwrenching, I can barely watch it. But so deserving of mention. When the dad is caught stealing, ugh....
Ok, a few more....
Treasure of the Sierra Madre (Huston '48) One of my all time faves, just gets better every time I see it. "We don't need no stinkin' badges", Walter Huston dancing the jig when they strike big, his warnings about greed, and Bogart, in what I think is his greatest role, slowly sliding into madness and paranoia. His fate just brutal. Great film.
Best Years of Our Lives (Wyler '46) US vets try to blend back into civilian life. Extremely blunt for the time this was made, honest in its portrayal of the difficulties faced by physically and emotionally handicapped men, and the wives and families trying to cope with it all. A late in film scene of Dana Andrews tipping perilously close to insanity while sitting in an abandoned bomber plane..... amazing stuff.
They Were Expendable (Ford '45) Probably my favorite 40's WWII film. Could've chosen a half dozen others from Ford. But rarely considered, this one is a rarity in that it shows the Americans on the losing end throughout. Story of the Phillipines, the evacuation of MacArthur, and the many soldiers and civilians left behind to face imprisonment and probably death at the hands of the Japanese. Mostly, this is about American PT boats that stayed behind to harass the Japanese army and which were all eventually lost. Mixed in with actual footage, a real feat for Ford to wrench so much emotion out of this.
White Heat (Walsh '49) Great Cagney gangster film. Cody Jarrett has bad headaches, bad temper, a mother complex (wait till he finds out in prison that she has passed on), Big Ed to worry about, a hot girlfriend, and serious paranoia. A real fun ride til' he gets to the "Top o' the world, ma!"
Duel In the Sun (Vidor '46) Land wars, brotherly jealousy over a woman, Lionel Barrymore, Gregory Peck as the bad brother, and Jennifer Jones
. Quite scandalous for the times but a great film.
Mighty Joe Young (Schoedsack? '49) Lovable Joe, similar to Kong. Joe loves hearing "Beautiful Dreamer". Fine effects from Harryhausen. Max O'Hara brings Joe back to the states. He also brought Kong back. Lets hope Joe doesn't meet the same fate
Lifeboat (Hitchcock '44) One of my favorite early Hitchcock. Survivors,after being sunk by a Nazi U boat, float in liferaft with the U boat captain.
Abbott & Costello Meet Frankenstein (Barton '48) Laurel & Hardy were fading, but A & C picked up the slack. This is probably their best film. It includes all 3 of the Universal mosters, Frankenstein, Dracula & Wolfman. Though not mentioned, Invisible Man pops up in the last scene
Kiss of Death (Hathaway '47) Sorta like White Heat. Richard Widmark in maybe his best role, also one of his first. He's a crazed psychopath criminal who is being set up by the cops, who use Victor Mature to do it. His laugh alone makes this one worth watching. Pushing granny down the stairs in her wheelchair is a bonus
The Egg & I (Erskine '47) Gotta throw in a screwball comedy. There were so many in the 30's and 40's. This one unleashed Ma & Pa Kettle on the public. Fred MacMurray and Claudette Colbert try to make a go of it on the farm. Right up there with all the other comedies.
I promise I won't write so much when we get to more recent times
Oh, and for all the Double Indemnity fans, I would highly recommend Sorry, Wrong Number. Very similar, but possibly more suspenseful.