WoWWiki - It's a wiki. About World of Warcraft. Um, It's a big wiki. with lots of stuff about World of Warcraft. Not much else to say.
Wowhead - Not the only database for WoW, but the best in my opinion. Good filters (Verigan's Fist is the only 2h weapon, not counting staves, that is rewarded from a quest and has spirit), stats that can be weighed, talent trees, a nice view in 3D button, in game links, and comments that are mostly useful. Also provides the tooltips for this blog.
Wotlk.wowhead.com - It's Wowhead. For the Wrath of the Lich King beta. Nuf said.
Warcrafter - A great way to play with gear, gems, talents, and enchants before you spend the time and money in game to get them. Wishlist support is also useful.
Be Imba! - Helps us lowly peons be uber by scanning your character and telling you that you forgot to enchant your bracers, your trinket is low level, and your gear is not ready for BT and Hyjal.
Armory Light - Just in case you want to check that pug mage's stats, but don't want to spend the time waiting for the official armory to load, we have this simple and fast loading version of the armory available.
WowJutsu - A raid progression tracker for those people who are into that kind of thing.
WotLK Information Wiki and Deathknight.info - Are you interested in WotLK or Death Knights? These are the places to go for information.
WOW Insider - I didn't want to list blogs here since the list would go on forever, but WOW Insider has just about everything in one blog. Updated by many writers throughout the day, you're sure to find something of interest to you.
P.S. If you work for WOW Insider and you read this blog, I'd love to write for you.
Elitist Jerks Forums - The place to go if you want to avoid the retched hive of scum and villainy that are the official WoW forums, and talk about hardcore theorycrafting and/or min-maxing. Be careful when you post, though, since you can rack up infractions and lose your posing privileges if you don't follow the rules.
Favorite infraction: "General Idiocy. You were being stupid and got called on it."
Curse Gaming - My website of choice for mods.