My vote is Fargo.
Casablanca Die Hard Goodfellas Good Will Hunting
Adaptation Network Cool Hand Luke
Only Charlie Kaufman can write a screenplay which turns into exactly what it didn't want to be.
Network - the great Paddy Chayefsky
Harry and Tonto La Strada One Flew Over the Cuckoos Nest Network Treasure of the Sierra Madre
Fight Club
The Hospital
Dr. Strangelove
Those bodily fluids really pushed the screenplay over the top.
In some ways I don't like the movie as much as I used to. As a vet I think the military is portrayed as a bunch of boobs. But overall it deserves a place among the great scripts.
Memento
To Kill a Mockingbird