The best writing books I've ever read

Over the years, I've read my fair share of writing books. Some were truly inspirational; others were so demotivating/intimidating that they made me want to give up forever. In no particular order, here are the three writing books I've found most useful:

• Writing the Novel: From Plot to Print, by Lawrence Block: This book tops the list for one reason. Unlike other novels, which put forward one way to do things and spend a lot of time insisting that any other method will result in failure, Block talks to a whole bunch of successful novelists and profiles their work habits. The inescapable conclusion is that there are a whole lot of wildly different ways to write a novel. He freely admits that if he had to follow some of the methods outlined here, he would have never finished writing a book.
• The Forest for the Trees: An Editor's Advice to Writers, by Betsy Lerner: This book is not a style manual or a how-to for novelists. In fact, the wisdom here applies equally well to fiction or non-fiction writers. Lerner takes you behind the scenes to the world of publishing. For novices who have unrealistic expectations of their editor, this book will set you straight about what you can expect from an editor, and what you should (and can successfully) push back on. A must-have for a writer pursuing publication.
• Writing a Romance Novel For Dummies, by Leslie Wainger: In the interests of full disclosure, I should note that my day job is as an editor/ghostwriter for the For Dummies series, although I work on technology-related titles only and had no involvement with the production of this book. That said, it is a fabulous book that offers what no generalized writing guide can: specific insights into what a top romance editor is looking for in a book. Her coverage of intellectual conflict versus emotional conflict alone is worth the price of the book. She distilled into words something I'd been half-heartedly sensing was wrong with my work for a long time. Although my characters always had conflicts that made sense on paper, they lacked the emotional conflict that is absolutely critical to a romance. Ms. Wainger gives a great example of a story that has intellectual conflict, but no emotional one: a tract of land well known as a refuge for the spotted owl is coveted by the heroine, a naturalist, for a wildlife refuge, but also by the hero, a developer, for a condo development. The book plods on, until the end, when they decide to set aside some of the land for a refuge and develop the rest. As Ms. Wainger points out, they have an intellectual conflict and think their way to a satisfactory resolution, but it's devoid of emotion. She tells you how to create conflicts that are rife with emotion.

These are three of the books I've found most valuable, but I'm sure other writers have some great recommendations as well. What have you found to be an invaluable help, and why?