www.wowhead.com

Wowhead is the greatest source of information for anything world of warcraft related. Get Quest info, check value of items, find the next best weapon or piece of armor for your level or class, or discover more things to do while wasting away in front of your computer playing the game that coined the word "Pwn". The simple search engine style of the site makes it a far cry easier than some of its competitors that are more well known. Thottbott and Wowwiki are also good for the information but sometimes a little harder to navigate through.

I personally use www.wowhead.com for all of my wow needs. If you use wowhead in conjunction with wowecon then you have info sources that can give you an edge over many noob players and help you gank rival players on the PvP servers. It also has helped me to start my Alliance Hunter Twink. He is only lvl 18 now, but he already has the deviate scale belt, the venomstrike bow, and plenty of decent other goodies. I am working now to farm for the mats to get all the enchants I need to make him near unstoppable in the level 19 battleground. Warsong Gulch is one of the most difficult at this level because so many do the same thing as me. However, with the extra info sources and a little time, I will get my twink above the rest to rival some players in twink guilds.