Even Blizzard bows knee to these guys ... they have data farmed the WoW servers more than Blizzard themselves and created a very easy to use bible about EVERYTHING Warcraft. There are guides for just about anything you could imagine, written with concise, easy to follow instructions, images and maps. Searchable databases with just about anything you could possibly imagine in the game. The community has also made this site a must go place with their years of input coupled with upgrading/downgrading moderation. If you need help this is the place to go first and foremost.
One of the longer lasting "How to Run your Class" website, this one tends to get the approval nod over the others from the world leaders in WoW gaming (ranked players). The layout is fairly easy to follow, leading you through a min/max buildout of your characters' class. Spec, gear, gemming, glyphing, rotation, it's all here. Despite the fact that it's written for the "hardcore" crowd, aspects such as talent spec breakdown and skill/spell rotation are so well explained anyone (even us super casuals) can improve their game just by reading up and learning to tweak your technique a tad.
A very easy to use (like dirt easy) guide for the fastest leveling of any of the professions. All the directions are simple, concise and listed in a format that almost screams "Duh" :) Excellent site to use even after you've leveled every profession to max time and again.
One of the better and easier to understand leveling guides out there. Step by step on what skills to take in your spec per level, where to go, how to level the professions and so on. The greatest part is that it doesn't feel like taking the game fun away, just helping you get leveled so even someone new could still enjoy the game while using this tool.
A fairly simple character building guide to get your toon running top condition at endgame. The interface is simple but they lack deeper explanations and they tend to follow "current fads" with padded data rather than pay real attention to the mechanics. Still it's an easy site to use and unless you are running hardcore or want to pull every cent out of the game's mathematics, this site will work well for helping your game.
A very solid gear upgrade comparison for fine tuning your endgamer to run dungeons and raids.
And for you hunters ... looking for a cool pet to tame? This website has it all in a simple format with lots of pretty pictures and information so you will know what you are looking for when you go to tame. Excellent place to find the right animals for your menagerie.