On Writing Well, by William Zinsser: An indispensable classic for anyone who writes or edits nonfiction, especially magazine articles and newspaper feature stories. The section on fighting clutter is a revelation. Re-read this book once a year.

The Elements of Style, by William Strunk, Jr., and E.B. White: All good writing begins with this tiny gem.

The New York Times Manual of Style and Usage: Although originally written just for the Times' editors and writers, this authoritative guide sets down rules that any newspaper-like publication would do well to live by.

The Chicago Manual of Style: As the book's subtitle says, an "essential guide for writers, editors, and publishers" on editorial style and usage—applying especially to book publishing.

The BBI Dictionary of English Word Combinations, compiled by Morton Benson, Evelyn Benson, and Robert Ilson: This book catalogues and explains the appropriate combinations of words in common usage. Sounds arcane until you're stuck trying to remember whether it's "amazed at" or "amazed by," or trying to choose among the varous verbs you can use with "damage."

The Non-Designer's Design Book, by Robin Williams (a different Robin Williams): No deep concepts here. But this guide does present basic principles about working with typography that are useful for editors to know. It might also help you communicate with your art director.