WoW Armory - The WoW Armory is Blizzard official information site where you can view any character on any realm. This includes gear, rep, skills, talents, ect...
WoW Head - Awsome database site containing lots of information on quests and skills. Loads better than Thottbot.
WoW Database - This new site popped up recently and is an interesting alternative to WoW Head and Thottbot.
WoW Census - check out the population of your favorite servers!
Thottbot - The google of WoW, it has drop rates, what drops what, skills for each classes, where monsters are, etc etc.
Petopia - has all the pet skills and where to get them listed. Also lists pets, and has some best possible choices.
World of Warcraft - the main site, crazy active forums.
CTmod - popular UI replacement mod
Cosmos - popular UI mod collection
WoW Vault - Great source for WoW info. Good community too. They also have a weekly segment called "Sprawls Crawl" which I encourage you to check out as it has the latest rumors, information, and other misc. info.
post any other links which are wow related(besides guild sites, and free servers, don't post those.)(well guild sites if they have something special)