Story: Substance, Structure, Style, and the Principles of Screenwriting
by Robert Mckee

A great tool to understand the art of story telling. McKee says anxious, insecure writers obey rules, rebellious writers break rules, artists master the form.

Screenplay: The Foundations of Screenwriting
by Syd Field

The Screenwriter's Workbook
by Syd Field

The Hero With a Thousand Faces
by Joseph Campbell

Myths to Live By
by Joseph Campbell

How to Write a Movie in 21 Days: The Inner Movie Method
by Vicki King

The Art of Dramatic Writing
by Laos Egri

Poetics
by Aristotle

John Truby
His tapes and other products are excellent.