With hundreds of screenwriting books on the market, on first browse it's hard to know good from bad. Here are the essentials.
The Writer's Journey
by Christian Vogler
A distillation of Joseph Campbell's The Hero with a Thousand Faces
applied to screenwriting. Vogler examines the Hero Quest, classic structure and the application of Jungian archetypes to character design. An essential read.
Story
by Robert McKee
The classic text deconstructing screenwriting structure.
Screenwriter's Bible: A Complete Guide to Writing, Formatting and Selling Your Script
by David Trottier
If you're looking for help formatting your screenplay, here's the bible.
Making a Good Script Great
by Linda Seger
A collection of well-crafted and insightful tips for the rewrite.
Advanced Screenwriting: Raising Your Script to the Academy Award Level
by Linda Seger
Whilst the title might be a little ambitious, here's another well-written book by Linda Seger, covering alternative structure, style and the functions of key scenes.
Screenwriting: The Sequence Approach
by Paul Gulino
The sequence approach to writing screenplays based on Frank Daniel's original work.
500 Ways to Beat the Hollywood Script Reader
by J. M. Lerch
Don't be put off by the title. An invaluable checklist for any script.
Writers' and Artists' Yearbook, 2007
by Ian Rankin
The annual roundup of literary agents, editors, publishers and competitions.
The Elements of Style
by Strunk and White
Grammar, composition and style. No writer should be without it.