http://www.calstatela.edu/centers/write_cn/sites.htm This site from Cal State has extensive links to other writing centers. The site is nicely divided into sources on the writing process, rhetoric and argument, grammar and mechanics, style, and documentation.
http://www.english.udel.edu/wc/resource/other.html From University of Delaware, this site has many links to university writing centers and style guides.
http://andromeda.rutgers.edu/%7Ejlynch/Writing/links.htmlJack Lynch's Resources for Writers and Writing Instructors is a popular web site, linking to his Grammar and Style Guide, Grammar Resources on the Web, and The Rhetoric Server from Berkeley. A rich and diverse web resource.
http://occ.awlonline.com/bookbind/pubbooks/aaronlbh_awlThis site links to The Little, Brown Handbook , which offers resources for students and instructors, including exercises and quizzes. It also has links to Addison Wesley Longman's The English Pages , a guide for literature and composition.
http://www.bedfordstmartins.com/hacker/writersrefThis site offers research guides in various disciplines, interactive exercises, and resources for composition courses.
http://www.amherst.edu/library/research/index.html The Frost Library's reference page has useful links to dictionaries, style guides, and guides to citation (including citation of Internet sources), and a link to the college's site on academic dishonesty and plagiarism