Preditors and Editors, hosted both by Anotherrealm and in Virtuo, lists agents, awards, publishers, contests, conventions, editing and copywriting, ghostwriting, software, email, jobs, journalism, magazines, music, organizations, screenwriters, signings, submissions, warnings, and workshops.
By far the most helpful thing about Preditors and Editors are the opinions. If an agent sounds too good to be true, check her out at P&E. If you want to know whether a publisher is legitimate, P&E is the place to go. Here's an example of a listing in the book publisher section:
AmErica House (aka PublishAmerica.com): PublishAmerica, Inc. contract formerly obtained all movie and book rights. Strongly not recommended. "A royalty publisher capable offering publishing contracts to all varieties of authors. Royalties paid, no fees ever charged, no agents required."
Nonfiction submission guidelines are included within the Journalism link. It took awhile to find them. I doubt it's a commentary on the genre, but rather a way to save bandwidth. P&E is much too direct to make a backhanded critique. Their honesty is refreshing.