WoWhead's Forums are awesome. I know we had a recent funny guild name post, but here are several from WoWhead that I don't believe made it. Add your own if it hasn't been mentioned. Enjoy.
Spaceballs The Guild - surprised this is the first time I saw this one
RPness is Rising
The Coming of Arwang
Fist is a Verb
Came Honor Face - say it quickly...
Sap It and Tap It
Fat Kids Are Hard To Kidnap - just plain awesome
GET OFF MY LAWN
She Said She was Lvl 18
Raging Horde On
Dont Daze Me Bro - far more clever than if it were "Taze"
Je Suis La Merde - "I am the shit" in French