The Curious Case of the Misplaced Modifier - How to Solve the Mysteries of Weak Writing by Bonnie Trenga is very useful. In fact it makes my list of writing books that every writer should own and use. Where Self-Editing for Fiction Writers deals with showing and telling and other editing problems, and the Writing the Breakout Novel deals with plot, tension and characterisation - this book deals with grammar and copy-editing. This is why I think it's a very useful addition to any writer's library.
It's slender, but packs a lot of punch for its size. The book consists of seven chapters and four appendices. Each of the chapters is dedicated to a common grammatical "crimes" found in writing from passive voice to wordy writing. The chapter starts with a passage written using the problemic form, and then explains why it's a problem and how to fix it. Finally as an exercise you are supposed to fix the passage at the start of the chapter. Really useful stuff.
The appendices are "the top ten writing misdemeanors" - ten other problems that weaken writing, an answer key for the exercises, a glossary and a "weak writing check sheet" that you can use as a quick reference when editing.
It's also well written. Grammar books are often dry and boring, but this one is light and often amusing. Especially the example passages which are so badly written it's hilarious.
Definately a book I highly recommend. Four Stars.