The following Web-sites serve as extensions of the FAQ page. Some of them focus exclusively on errors while others offer grammar and usage advice and information on writing styles. Please refer to these sites before going to Ask a Question.
alt.usage.englishFAQ (Mark Israel): Etymologies and usage issues are provided along with "phrase origins" and "miscellany" sections.
Common Errors in English (Paul Brians): A site "dedicated to errors in usage [,...] not a site dealing with grammar in general" (Brians).
Commonly Confused Words: Gives definitions and examples of words that are misused because they sound alike or are similar in spelling.
Dictionary.com Word FAQs: Go to the "Grammar/Usage/Style" section for useful information.
Guide to Grammar and Style (Jack Lynch): Information compiled for Lynch's classes about rules of grammar, style, and usage.
Guide to Grammar and Writing: Click on "Index," scroll down, and click on "Notorious Confusables." Part Two is a continuation of Part One.
Purdue Online Writing Lab (OWL): Grammar, spelling, and punctuation handouts are available along with other useful information.
Wordorigins.org (Dave Wilton): Learn about word and phrase origins.