This one (onetwothreefour) from Silence of the Lambs always sticks out in my head:

"almost at point-black range, guns ROARING hugely, one FLASH from Mr. Gumb, and onetwothreefour FLASHES from Clarice, overlapping his, and then, as the ECHOES crash deafeningly -"

Not "Four flashes from CLARICE" but "onetwothreefour flashes from CLARICE"

Love it.

Thanks guys, great examples. I've always liked the scene description from Alien when the xenomorph bursts out of Kane's chest.

A red stain.
Then a smear of blood blossoms on his chest.
The fabric of his shirt is ripped apart.
A small head the size of a man’s fist pushes out.
The crew shouts in panic.
Leap back from the table.
The tiny head lunges forward.
Comes spurting out of Kane's chest trailing a thick body.
Scatters fluids and blood in its wake.
Lands in the middle of the dishes and food.
Wriggles away while the crew scatters.
Then the Alien being disappears from sight.
Kane lies slumped in his chair.
Very dead.
A huge hole in his chest.
The dishes are scattered.
Food covered with blood.

The use of short sentences here really punctuates the action and the horror of the scene.