Hey some very good sites I used during my play in World of Warcraft.
MAXDPS.com
This site above will easily show you how to improve your dps through great cast rotations and shows gear upgrades by you placing in AP,SP,HASTE,CRIT ect...
http://www.arenajunkies.com/ (Thanks ToR)
For the PVP enthusiast in all of us. You learn all the tricks of the trade in this one . what the best combos are to what spells and classes counter what.
http://www.wowinsider.com/ (Thanks ToR)
Blog dedicated to the rich and addicting universe of World of Warcraft. Posts include how-tos, tips and tricks, patch updates, and more
Elitestjerks.com
Very intense number spam about characters they can tell you good bad and ugly about every class and will tell you how to WTF pwn with your character just don't be a noob. Use the search button.
Worldofraids.com
This site shows updates with the patchs and a lot of usefull information.
I had gotten a request about a good tanking site like Maxdps.com. Well I asked a few tank friends and they said.
www.tankspot.com
Offers blogs, podcasts, forums and FAQs on tanking (mainly warrior-specific)
WoWhead.com
WoW database covering items, NPCs, objects, quests, spells, and zones. Also has current and Burning Crusade talent calculators, and an add-on to upload data
Each of these sites helped me be a very great player at the game including this one. I raided Every instance in the game with these sites in my hand.
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Update to 1-21-09