Author Dan Pink posted recently on his top 5 favorite books on writing. It's especially interesting to see what Dan's picks are for this as his new book is in a very unique format for the Western business book world: manga. Writing is tricky enough alone, but in his case, Dan had to condense everything, and let a lot of the message be communicated by visual illustrations. I'm sure it was a process for him to think differently about what he was going to say, and reduce it to a concise statement that could fit within a series of quick talk bubbles coming from the mouths of the characters in the story.
Nonetheless, his picks for books on writing are dead-on, whether you're writing essays, novels, or comics.