*Characters and Viewpoint (of course!) by Orson Scott Card. An absolute must-read. He also did one on Fantasy & SF writing which is good, though I think slightly less essential.

*On Writing by Stephen King. I've never really read much of his other stuff, but this one was great. Mainly biographical, but very good at motivating you for the needed perseverence in writing. He does offer some good practical tips as well.

Speaking of Card, the book "How to Write Science Fiction and Fantasy" is his other great writing title.

I liked the book and got some useful advice out of it. Frankly, I think the advice to be able to use grammar well and without thinking about it is good advice. While I hesitate to contradict OSC on his own site, I think the reason he doesn't see that as good advice is because he doens't have to think about grammar. I don't think OSC realizes that the words come to him with less effort than they come to other people.

And everyone's brain works differently. For some people King's book will be very useful.

My favorites so far have been (besides OSC's two, which are excellent):

Self-editing for Fiction Writers by King and Browne

Beginnings, Middles, and Ends by Nancy Kress

And one that I consider more a book of wisdom and reassurance (writer's chocolate, if you will)that a how-to book:

The Writer's Mentor by Kathleen Rountree

Because King can do that, he doesn't realize that while his approach to writing, which is to put a character in an interesting situation and let things happen on their own, works for him, it may not work as well for someone who has a harder time creating interesting characters.

Whenever you read a "how-to-write" book by a successful author, you need to remember that the author will not be able to tell you how to do the things the author does automatically and without having to think about them.