Gabriele Lusser Rico, Writing The Natural Way. I think it's similar to the "Bones" books, various exercises to get the mind operating creatively. Techniques used cover clustering, image and metaphor, re-vision, creative tension and language rhythm.

Kathryn Lindskoog's Creative Writing, for People Who Can't Not Write. Great, inspiring, book discussing the art of writing from perspectives I haven't entirely seen elsewhere. Time for a re-read!

L. Sprague & Catherine de Camp, Science Fiction Handbook. It's old enough that the marketing information is not to be relied on, but the writing advice is timeless.