We asked our Bad Language columnist Matthew Stibbe to recommend his favorite books on writing well. Check them out, plus read his reviews.
Writing to Deadline by Donald M. Murray (Matthew's review)
The Economist Style Guide (Matthew's review)
The Pyramid Principle by Barbara Minto (Matthew's review)
The Elements of Style by William Strunk, Jr. ("The obvious choice," says Matthew. But timeless -- and small enough to fit in your pocket. His review.)