There are a lot of sites out there that put together information that is meant to be useful to writers. However, while many of them are started with the best of intentions, they are quickly left to rot in cyberspace. In other cases, you have to pay to obtain any useful information. These sites are well-tended, free and updated frequently. (These links will take you off-site.)
Writing for the web
A web-zine devoted to the discussion of online writing and content. It is also home base for an e-mail discussion list (lserv) that is designed to be a forum and idea-sharing space for writers and editors who work, or want to work in this medium.
Essential for journalists
American Journalism Review and Investigative Reporters and Editors
Industry information and trends, worthwhile classifieds, links galore. Both of these sites contain indispensible information that will keep you abreast of current ethical dilemmas in journalism, new publications that have cropped up, and much more.
What the Editor Wants from you, Aisle 3
A web extension of the annual Writer's Market, this site contains updated, searchable writer's guidelines for huge, honking, glossy mags as well as itty-bitty e-zines. It also has articles about writing queries, selling manuscripts and composing saleable stories that are sometimes helpful, but the market listings are the most useful component of this site.