Grammar and Usage

American Heritage Book of English Usage: "Practical and Authoritative Guide to Contemporary English" with a detailed look at grammar, style, diction, word formation, gender, social groups and scientific forms. Valuable reference for students, writers, academicians and anybody concerned about proper writing style. Part of Bartleby.com .
The American Language: An Inquiry into the Development of English in the United States, 2nd ed.: H.L. Mencken's 1921 classic discusses the differences between British and American English and defines the distinguishing characteristics of US English. Part of Bartleby.com.
The Book of Clichés: "Phrases to say in times of trouble," arranged by category. One of the classic cliché-sites, winner of numerous awards.
Cliché Finder: Searchable index of more than 3,300 clichés. You might like to visit a companion site, Smugopedia, "a collection of slightly controversial opinions about a variety of subjects."
Common Errors in English: Identifies costly mistakes in writing and speaking English, as judged by professional writers, editors, teachers. Alphabetically arranged with handy index. Part of a larger site containing other language-related info, Home Page of Paul Brians.
The Elements of Style: William Strunk, Jr. called this his "little book" on the principles of English style and grammar. The Elements of Style has become an American classic. Part of Bartleby.com.
Grammar and Usage for the Non-Expert: A range of articles intended to solve common problems of grammar and usage for those who want answers but don't want a lot of technical explanations.
Guide to Grammar and Writing: Contains scores of digital handouts on grammar and English usage, from word choice through the building of larger units, computer-graded quizzes, powerpoint presentations and much more, covering seemingly every aspects of the subject.
Hypertext Guide to English Grammar, Mechanics, and Usage Rules: Exactly what it says. Part of a comprehensive Virginia Tech program.
The King's English, 2nd ed.: H.W. Fowler's 1908 work with commonsense rules of style and grammar remains a standard resource for generations of students and writers. Still another part of Bartleby.com.
perfectyourenglish.com: Extensive free online reference guides to English Grammar, Practical English usage, vocabulary, English writing and speaking. Includes interactive grammar and vocabulary exercises.
The Vocabula Review: Journal about "the devolution of language." Discourages nonstandard, careless English and encourages clear, expressive English. Large collection of essays, hints and tips.