the best last shot in a film?

Stalker with the moving glass shot.
Citizen Kane with the Rosebud explained.

On the Beach - "There is still time... Brother".

Psycho - The transition from Norman to the car, with the superimposed skull.

Well, it's not technically the last shot, but I'm going with Slim Pickens enthusiastically riding the atomic bomb at the end of Dr. Strangelove.

House of Flying Daggers (2004). A movie only saved entirely by one last scene.

Resident evil chapter.

The Thing.

Citizen Kane
Baby Jane
Strangelove...meaning the true last shot
Third Man
Casablanca
Silence Of The Lambs

Hm, The Usual Suspects isn't really a shot.

The last shot of Scream gives me chills. The combo of an early dawn sky and the background music, together with the tragic events that just transpired, is just perfect.

Disney animations often have great last shots as well. BatB, Pocahontas, even Finding Nemo.