Kenneth Wilson 
The Columbia Guide to Standard American English [PDF ebook] 

In the most reliable and readable guide to effective writing for the Americans of today, Wilson answers questions of meaning, grammar, pronunciation, punctuation, and spelling in thousands of clear, concise entries. His guide is unique in presenting a systematic, comprehensive view of language as determined by context. Wilson provides a simple chart of contexts—from oratorical speech to intimate, from formal writing to informal—and explains in which contexts a particular usage is appropriate, and in which it is not.
The Columbia Guide to Standard American English provides the answers to questions about American English the way no other guide can with:
* an A–Z format for quick reference;
* over five thousand entries, more than any other usage book;
* sensible and useful advice based on the most current linguistic research;
* a convenient chart of levels of speech and writing geared to context;
* both descriptive and prescriptive entries for guidance;
* guidelines for nonsexist usage;
* individual entries for all language terms.
A vibrant description of how our language is being spoken and written at the end of the twentieth century—and how we ourselves can use it most effectively—The Columbia Guide to Standard American English is the ideal handbook to language etiquette: friendly, sensible, and reliable.