Bly, Carol. The Passionate, Accurate Story. Milkweed, 1998.
It’s intended for fiction writers, and it can be bewilderingly academic and political at times, but there’s interesting stuff here for essayists to consider.

Clark, Roy Peter. Writing Tools: 50 Essential Strategies for Every Writer. Little, Brown 2008.
A book that examines everything from sentence structure to finding ideas.

Goldberg, Natalie. Writing Down the Bones: Freeing the Writer Within. Expanded version, Shambhala 2006.
If you’re having trouble getting started with freewriting, this book will shake it out of you.

Gornick, Vivian. The Situation and The Story: The Art of Personal Narrative. Farrar, Strauss & Giroux, 2002.
Incredibly useful for essayists and people interested in writing narrative.

Hulme, Peter (Editor). The Cambridge Companion to Travel Writing. Cambridge University Press, 2002.
An academic look at travel writing that can be a little dry but at times inspirational.

Kramer, Mark and Wendy Call. Telling True Stories: A Nonfiction Writer’s Guide from the Nieman Foundation at Harvard University. Plume, 2007.
A distillation of wisdom from the many noted writers that have presented at the Nieman conference over the years; Adam Hochschild’s short essay on travel writing is worth the price of the book.

McClanahan, Rebecca. Word Painting: A Guide to Writing More Descriptively. Writer’s Digest, 2000.
Excellent break down of description and many exercises to build description muscles

McKee, Robert. Story: Substance, Structure, Style and The Principles of Screenwriting. Harper, 1997.
Movies and television are the dominant narrative form of our time, and McKee analyzes and explains how it’s done quite brilliantly, if a bit incoherently at times.

Oliver, Mary. A Poetry Handbook: A Prose Guide to Understanding and Writing Poetry. Harcourt Brace, 1994.
Focuses on the technical concerns of creating poems, great for any writer concerned about putting the right words in the right order.

Oliver, Mary. New and Selected Poems, Volume One. Beacon 1992.
Mary Oliver writes poems that are lovely images of the observed world, and are great inspiration for note-taking.

Pressfield, Steven. The War of Art: Break Through the Block and Win Your Creative Battles. Grand Central, 2003.
Essential reading for every writer, strategies for how to resist resistance.

Vogler, Christopher and Michael Montez. The Writer’s Journey: Mythic Structure for Writers, 3rd Edition. Michael Wiese Productions, 2007.
Although intended for screenwriters, excellent for understanding the most common narrative structure.

Zinsser, William. They Went: The Art and Craft of Travel Writing. Houghton Mifflin, 1991.
This is out-of-print but worth tracking down, “writers who travel”, rather than travel writers, discuss their work and how they did it.