Brown, Rita Mae, Starting From Scratch: A Different Kind of Writer's Manual
The chapter on Anglo Saxon and Latin is especially useful.

Burnham, Sophy, For Writers Only
Easy to dip into. Wise words.

Cameron, Julia, The Artist's Way
New Agey and at the same time highly practical.

— , The Sound of Paper: Starting from Scratch
Thoughtful, elegant, and inspiring mini-essays.

Dillard, Annie, Living by Fiction
A book about the world.

Flack, Audrey, Art & Soul: Notes on Creating
Deep. The artist as shaman.

Friedman, Bonnie, Writing Past Dark: Envy, Fear, Distraction, and Other Dilemmas in the Writer's Life
From the trenches.

Goldberg, Natalie, Writing Down the Bones: Freeing the Writer Within
A very popular book. Packed with fun writing exercises.

Iglesias, Karl, The 101 Habits of Highly Successful Screenwriters: Insider Tips from Hollywood's Top Writers
I'm not a screenwriter (yet), but I love this book. It was like reading about distant but kindred tribe. Lots of useful tips.

Lamott, Anne, Bird by Bird: Some Instructions on Writing and Life
Hilarious. For anyone at any stage in their writing.

Leonard, George, Mastery: The Keys to Success and Long-Term Fulfillment
Zen.

Maisel, Eric, PhD., Fearless Creating: A Step-by-Step Guide to Starting and Completing Your Work of Art
Dr Maisel specializes in helping artists, and he's a prolific writer himself. There is a great deal of wise advice in this book.

Pressfield, Steven, The War of Art: Winning the Creative Battle
The best. If you're blocked and you want to buy one book to help yourself, this is the one.

Ricco, Gabriele Lusser, Writing the Natural Way: Using Right-Brain Techniques to Release Your Expressive Powers
Revolutionary. (Note: this is also on my list of recommended books on craft.)

Rhodes, Richard, How to Write: Advice and Reflections
Good advice from a highly accomplished and prolific writer.

See, Carolyn, Making a Literary Life
Good advice from another highly accomplished and prolific writer -- this one from LA. It's a hoot.

Ueland, Brenda, If You Want to Write: A Book About Art, Independence and Spirit
A classic. Very popular with many of my writing workshop participants.