On Writing: A Memoir of the Craft, by Stephen King – My favorite book on the writing process, written by a master.
The War of Art: Break Through the Blocks and Win Your Inner Creative Battles, by Steven Pressfield
Writing Down the Bones: Freeing the Writer Within, by Natalie Goldberg
Zen in the Art of Writing, by Ray Bradbury – An insightful book on how it is done by a highly successful – and human – career author.
The Chicago Manual of Style: The Essential Guide for Writers, Editors, and Publishers, University of Chicago Press
Smashwords Style Guide, by Mark Coker – Extremely helpful formatting tips for creating ebooks. Much of the information applies to Kindle formatting as well as epub.
Writing Nonfiction: Turning Thoughts into Books, by Dan Poynter – Despite its title, this is one of the first – and best – books on combining self-publishing of your book with your business goals.
1001 Ways to Market Your Books, by John Kremer
Content Rich: Writing Your Way to Wealth on the Web, by Jon Wuebben – This is a pretty good introduction to Search Engine Optimization for your website.