After George's encounter with his alternate universe mother, the close-up of him slowly turning toward the camera in sheer frustration and terror is enough to send a chill up anyone's spine.
Everything that happens to George in the alternate reality, really.
The scene when George stumbles into Pottersville is like an episode of The Twilight Zone.
The scene where George comes home and yells at his wife and kids is frightening in a whole different way.
Everything during George's slow mental breakdown over the loss of the money is probably the movie's darkest point. Especially when he's officially been Driven to Suicide, the way he walks in the street and towards the bridge without noticing anything around him at all.
The deleted scene involving Clarence lecturing Mr. Potter and giving him a heart attack does sound pretty chilling, even if the villain is getting his comeuppance.
The look on George's face right before he jumps is rather unsettling.