I studied a lot of books on writing when I was at university, and I think the one I found the most helpful was called 'The Making of a Poem' by Evan Boland. It is a Norton Anthology of Poetic Forms, which describes, explains, and provides several examples of several types of poetry, including sesitinas, villanelles, sonnets, ballads, blank verse, and free verse. It tells you the history of how each was formed, and gives you a step by step guide on how to write them.
A book called Wired for Story by Lisa Cron is fantastic - it looks at the neuroscience behind stories and story telling, and how writers can utilise that to make their story even more compelling for readers.
Aristotle's Poetics. It sounds like I'm just being a wanker, but its advice is clear ('Begin your story at the point where it all starts!' 'Don't feel the need to include every little detail in your story - skip what doesn't fit the theme or mood!'), it's short (~40 pages) and it's about 2,500 years out of copyright, so you can pick it up very cheaply and easily.
I like A Moveable Feast, which is not so much a how to, but a here's how 2 great authors did it very, very differently (though both drunk a lot of the time - maybe that's the secret). I also have Michael Chabon's Reading & Writing, but not read it yet...
When I was writing every day and every week, I was handed a copy of Stephen Kings "on Writing". Together the true value of this book you have to cut through the first halve of the book (which is, needless to say a brag sheet), move directly to the page titled "On Writing" From there it talks about developing a tool kit and such it also talks about influencing and Muse's. It is a tool I have used to help me re-engage with writing and more importantly communicating.