Picked up a book yesterday that has already borne fruit re: my writing. The Writer's Journey by Christopher Vogler. Vogler has taken Dr. Campbell's The Hero With a Thousand Faces and explains how to incorporate mythic structure and archetypes into stories and screenplays. I'm not even halfway through the book and already I've used it to do an outline for my next book that's a hundred times better than the goop it was before.

Seriously, if you want to write science-fiction or fantasy you need this book.