Reckoning (US) »
Firetree is an EST US PvP server founded February 24 of 2005, among the first wave of new servers established after the game was released. Currently houses Pie Chart guild ranked as #13 in the United States.
Firetree consists of a great community, small enough so everyone knows each other, but large enough to house many great guilds.
For Facebook users you can find a growing community at 
Horde: Horde has, for a long time, struggled to maintain a unified position on almost any front. (With the exception of pre-rushing Alterac Valley in which Horde enjoyed superiority for years at a time using the Preform AV Enabler Add-On) Before the Burning Crusade, Horde PvE was significantly stifled, due to continual spats and disagreements between capable players and capable leaders. While they lacked a unified vision to go after dungeon objectives, they compensated with a fierce continual world and Battleground PvP presence that was never to be underestimated. When world PvP died out it was Ave Satanas and Smakaho Tribe that brought it back. With the drastic changes to game mechanics brought by the Burning Crusade (specifically 10-man raiding teams), Horde PvE progression has accelerated to unprecedented levels. Being able to work in smaller raid sizes, Horde guilds such as Cake and No Life were able to become of the greatest guilds of the server.
Alliance side: Firetree’s community has maintained an enigmatic appeal that has kept many of the original players on the server for several years. In the very early days, many guilds reshuffled their power structures due to raid loot disputes and personal animosity, but nothing to the severity of Hordeside politics. Even amidst restructuring, PvE progression was still being done at an acceptable rate with a good number of Alliance guilds. Aside from the notable exceptions of the Chosen/Lucky Strikes/Arc three-capital assault (that crashed Kalimdor) and the Chosen/Lucky Strikes assassination of Thrall, Alliance world PvP has been sporadic at best. Alliance has focused on PvE in such detail that many advanced guilds offer pick-up spots for non-guilded members to partake in as well as offering them loot.