Seriously, what is the rule for semi-colons? 😛 Here’s a website on it, since we’re talking about editing resources 
English Language & Usage (website)Great and usually very accurate when it comes to the finer points of grammar. Suggested by http://amosmcarpenter.com/
Sin and Syntax, Constance Hale. It’s informative but not boring. Suggested by 
Amazon people say: “Today’s writers need more spunk than Strunk: whether it’s the Great American e-mail, Madison Avenue advertising, or Grammy Award-winning rap lyrics, memorable writing must jump off the page. Copy veteran Constance Hale is on a mission to make creative communication, both the lyrical and the unlawful, an option for everyone. With its crisp, witty tone, Sin and Syntax covers grammar’s ground rules while revealing countless unconventional syntax secrets (such as how to use—Gasp!—interjections or when to pepper your prose with slang) that make for sinfully good writing.” (Written by American)
Writing Tools: 50 Essential Strategies, Roy Peter Clark. It takes a more positive stance, instead of “don’t do that.” Suggested by http://loyalmuse.wordpress.com/
Amazon: “WRITING TOOLS covers everything from the most basic (“Tool 5: Watch those adverbs”) to the more complex (“Tool 34: Turn your notebook into a camera”) and provides more than 200 examples from literature and journalism to illustrate the concepts. For students, aspiring novelists, and writers of memos, e-mails, PowerPoint presentations, and love letters, here are 50 indispensable, memorable, and usable tools. ” (Written by American)
Revision and Self-Editing for Publication, James Bell
“In Write Great Fiction: Revision & Self-Editing, James Scott Bell draws on his experience as a novelist and instructor to provide specific revision tips geared toward the first read-through, as well as targeted self-editing instruction focusing on the individual elements of a novel like plot, structure, characters, theme, voice, style, setting, and endings.”
Grammatically Correct, Anne Stillman
Amazon says: Covers topics including: spelling variations, hyphenation, frequently misused words and phrases, irregular plurals and negative, punctuation, syntax and structure, agreement of subject and verb, tenses, active versus passive voice, clarity/tone, sentence length and order, and much more. It claims to steer clear of academic stuffiness, focusing instead on practical strategies and intuitive explanations.
The Elements of Style,Fourth Edition, by Strunk and White
Here’s what Amazon says: “You know the authors’ names. You recognize the title. You’ve probably used this book yourself. This is The Elements of Style, the classic style manual, now in a fourth edition. A new Foreword by Roger Angell reminds readers that the advice of Strunk & White is as valuable today as when it was first offered.This book’s unique tone, wit and charm have conveyed the principles of English style to millions of readers. Use the fourth edition of “the little book” to make a big impact with writing.”
Self-Editing for Fiction Writers, R.Browne D.King
According to Amazon: “In this completely revised and updated second edition, Renni Browne and Dave King teach you, the writer, how to apply the editing techniques they have developed to your own work. Chapters on dialogue, exposition, point of view, interior monologue, and other techniques take you through the same processes an expert editor would go through to perfect your manuscript. Each point is illustrated with examples, many drawn from the hundreds of books Browne and King have edited.”
The Penguin Writer’s Manual (Penguin Reference Books) According to a writer in my Singapore Writer’s Group: a bit of everything: typical grammar mistakes, punctuation errors you spell check won’t notice, elements of style. Compact and easy to understand.
Amazon claims: The Penguin Writer’s Manual is the essential companion for anyone who wants to master the art of writing good English. Whether you’re composing an essay, sending a business letter or an email to a colleague, or firing off an angry letter to a newspaper, this guide will help you to brush up you communication skills and write correct and confident English.