Grammar

• The Blue Book of Grammar and Punctuation - The online version of this popular book, which is an indispensable and entertaining guide for writers, proofreaders, editors, managers, clerical staff, teachers, and students.
• Common Errors in English - Common Errors in English is concerned only with deviations from the standard use of English as judged by sophisticated users such as professional writers, editors, teachers, and literate executives and personnel officers. The aim of this site is to help you avoid low grades, lost employment opportunities, lost business, and titters of amusement at the way you write or speak.
• Guide to Grammar and Writing - Includes definitions of sentence parts, rules for comma usage and other punctuation marks, plurals and possessives, spelling, nouns and modifiers, words and phrases to avoid, capitalization, spelling and abbreviations, and a lot more.
• The Nuts and Bolts of College Writing - A very thorough site on how to improve your writing.