The post mentioning Stephen King's ON WRITING drew a lot of positive feedback in the comments and the emails, so I thought I would throw out a few other books that help me throughout my writing process.
One great resource is THE 3 A.M. EPIPHANY by Brian Kiteley. It's a book that is loaded with exercises to try and get you thinking outside the box. Kitely is a creative writing prof at the University of Denver, and the thing this helped me a lot with is writing tighter.
Struggle with dialogue? Then you gotta read LUSH LIFE by Richard Price. It's not a help book, but he's a master of writing dialogue. Reading that book showed me ways to use dialogue differently, ways to use different voices and it just plain helped me in that department. Besides, it's a damn good book.
One of your characters missing something? Check out WRITER'S GUIDE TO CHARACTER TRAITS by Linda Edelstein. This book won't tell you a better way to write characters, but it will show you how to give them more layers. This book helped me make my characters seem more realistic.
Those are just a few. Of course, one of my tips for any kind of writer is to read, read, read. Then take a nap, write and read some more.
Anybody else have some good resources that helped you in your writing? Share them in the comments for everybody. Go on. Don't be bashful.