Combined with Thottbot this is a treasure of info for every player, experienced or not. Not only does it list 99,9% of the quests available in-game there is so much information about the world that it can be mind-boggling.
Easy to navigate and it provides links and suggestions to other helpfull sites within it's articles.
A MUST for every WoW noob out there.

Have recently started using this site. It's good for general information. Used it for rep quest guides and daily quest chain info

Even though it can contain inaccurate information, it's easy to use and can help out a lot on more general areas.
Particularly useful for me recently were the Lockpicking guide, Leatherworking guides (finding the trainers and advice on which to specialise in)
As with all wiki's it can be misleading but on the whole helpful when combined with other sources of info