Great Last Scenes: Sunset Boulevard

Year: 1950
Director: Billy Wilder
Great Because... not only does it provide a fittingly dramatic exit for a larger than life character, it also manages a delicate mixture of tones: it's sad, flamboyant and creepy as hell all at once (you could also argue that it's triumphant, albeit as the triumph of madness over sanity). Most importantly, it's an ending that stands up to multpile viewings:

In a fit of desperation former screen star Norma Desmond has killed her lover, Joe Gillis. In the ensuing media circus, Norma’s tenuous hold on sanity is finally and definitively broken, and she comes to believe that the hubbub in her foyer is a cast and crew preparing for a scene in her comeback vehicle.

Seeing the cameras, Norma descends the staircase into infamy and insanity, stopping only to express how much the moment means to her:

I just want to tell you all how happy I am to be back in the studio making a picture again! You don't know how much I've missed all of you. And I promise you, I'll never desert you again because after Salome we'll make another picture, and another picture! You see, this is my life. It always will be! There's nothing else - just us - and the cameras - and those wonderful people out there in the dark. All right, Mr. De Mille, I'm ready for my close-up.

Finishing her speech, Norma begins to move towards the camera - and us. Looking directly through the camera to the audience, the message become clear: Hollywood may be partially to blame for breaking Norma, but the audience is just as guilty. Fade to black.