Thottbot

It goes without saying that Thottbot is the most useful tool for completing quests quickly and investigating items.

http://www.thottbot.com/

WoWwiki

WoWwiki is another tremendously useful site for anything WoW related.

http://www.wowwiki.com/Main_Page

Instance Information

I use WoWwiki primarily for researching instance strategy and seeing what Bosses drop which loot. Below is a link to the WoWwiki Instance page.

http://www.wowwiki.com/Instance_guide

World of Warcraft Add-Ons

Some members are not sure where to get the WoW Add-Ons such as the map co-rodinates, Auctioneer, Gatherer etc. I believe most are obtained from Curse Gaming. Download the Add-On you are after and unzip it into your WoW Interface/AddOns folder.

http://wow-en.curse-gaming.com/downloads/addons/

World of Warcraft Armoury

Most of us know about this but for those who don't the WoW Armoury site is where Blizzard's information on every WoW player is stored. Search for your character, our Guild or for the Horde Rogue who keeps ganking you. It shows all the stats, gear, skills, etc.

http://armory.worldofwarcraft.com/

Enchanting

Thottbot has a list of all the currently available enchants and what mats are required. If you are after a particular enchant check out this page and start collecting the mats. If you are a couple short check the AH or ask one of the Guild Enchanters.

http://www.thottbot.com/?t=Enchanting

World of Warcraft Forums

If you have a question that can't be answered by your Class Captain or you just want to research some options the WoW Forums are your best bet.

http://forums.worldofwarcraft.com/index.html?sid=1