Like most writers, I have quite a few on the subject and some I wished I hadn't wasted my money. Not that the authors didn't know what they were talking about, they were just boring. I will say if someone recommends a writing book, be sure they have a copy and use it often. Buyer beware if they say, "I heard that's a good one" but don't own it. I bought one on that recommendation and regretted it. Who has $10 to $25 to waste?
So remember, most people won't recommend a book they own and don't like.
One I suggest you check out is SAVE THE CAT! by Blake Snyder. I like his style of explaining things. It's easy to read and he has a quirky sense of humor. The book is actually for screenwriting but it can be applied to novels without a problem. I bought it when I read on another blog (can't remember whose) how excited the woman was about the book. She even claimed it helped her become published. So who can ignore that recommendation?
I do have several more I enjoy and use that are for storytelling in general, like THE WRITER'S JOURNEY by Christopher Vogler, CREATING CHARACTER EMOTIONS by Ann Hood and THE ELEMENTS OF STYLE by William Strunk, Jr. and E.B. White.
What book(s) on writing do you find to be most useful?