The Shawshank Redemption definitely has the most satisfying ending, but i would nominate the following endings:
Dog Soldiers - With his unit wiped out, as well as the titular werewolves, Private Cooper is confronted by the machiavellian Captain Ryan in a cellar, who has turned very hairy and savage. A useful distraction from border collie Sam, followed by Cooper stabbing Ryan with a silver letter opener and then a bullet to the head equals a very satisfying ending.
Batman Begins - Batman meets Lieutenent Gordon on the rooftops, discussing the future for Gotham. The Dark Knight is given a familiar playing card, promising to investigate as he disappears into the night. Satisfying, it brought the Bat back.
Trainspotting - Renton absconds with the 16,000 grand obtained from the heroin transaction, while the psychotic Begbie smashes up a hotel room in a fit of rage. It's satisfying because it shows Renton promising to go straight and live a normal life.
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"I've seen things you people wouldn't believe: Attack ships on fire off the shoulder of Orion; I've watched c-beams glitter in the dark near the Tannhauser Gate. All those moments will be lost in time; like tears in rain. Time to die." Roy Batty