Which MMO developers know how to mesh with their customers and put out awesome comprehensive wikis?
My two favorites are:
http://wiki.eveonline.com/en/wiki/Main_Page
http://wiki.guildwars2.com/wiki/Main_Page
It seems like a no-brainer way to hook new players in to the game mechanics and lore, but some of the major MMO's don't do it.
Yes, I'm looking at you Rift and WoW!