There are several community-run wow-related discord servers, including this one for WoW in general and these for each class. Check these channels if you want to stay tuned for the very latest theory-crafting. You can also make a free server for your guild.
http://www.icy-veins.com/wow/class-guides – A very reasonable starting off point for class guides, with the best guide available for some specs. The Icy-Veins forums also have bits of useful discussion.
http://www.reddit.com/r/wow/: This reddit subreddit is an official wow community site and has good, active discussion about wow.
http://www.reddit.com/r/CompetitiveWoW/: This reddit subreddit is narrowly focused on high-level wow raiding. There are detailed guides, log analysis posts, and more.
http://simplearmory.com/: This website allows an alternative view of the wow armory. The collectibles, mounts section links to a good guide for mount farming and tells what you missed at a glance.
http://bossblueprint.com/wow: This website is a great way to quickly outline raid positioning strategies for HFC.