If I may hijack your reply for a recommendation thread, I'd recommend "The Sense of Style" by Steven Pinker, too. It's worth it just for the section on metaconcepts. I loved how much simpler my writing became when I removed them.
Also, read anything by Robert Graves. He did write a style guide called "The Reader Over Your Shoulder", but that's optional; I learned far more about good writing from "I, Claudius" and "Good-Bye to All That".
- On Writing Well by William Zissner
- Several Short Sentences About Writing by Verlyn Klinkenborg
- The Elements of Style, 4th Edition by Strunk & White
- Good Prose by Kidder & Todd
- Wordcraft by Jack Hart
- Storycraft by Jack Hart
- The Art and Craft of Feature Writing by William Blundell
- The Art and Craft of Storytelling by Nancy Lamb