Treasure of the Sierra Madre

An IMDb Top 250 movie

Greed corrupts, as Humphrey Bogart, Walter Huston (director John Huston's father) and one Tim Holt discover in this classic about gold-digging. Huston plays a seasoned prospector, who knows enough about human nature to realize that (a) whoever you dig with will do anything to get hold of your gold and (b) he himself is no exception to rule (a).
Bogart's character, on the other hand, new to the trade, turns from hopeful to angry to homicidal as his grasp on the gold tightens and weakens. It's one of his better roles.
Quite aside from the good cast and script, I was also delighted to finally find out the origin of that classic phrase: "Badges? Badges?! We don' need to steenkin' badges!" Like so many movie quotes, this one is different from what is actually said in the movie (by a Mexican desperado posing as a policeman, being asked for his badge by Bogart).