if your going the holy trinity route (1 tank 1 healer 1 DPs) then Id suggest this.

Unholy DK - 13% magic dmg and a good aoe tank
Frost mage - most aman efcient spec and strong aoe, note you want this with the DK for sure simply becuase the DK wil give a melle slow on the target at all times and with torment the weka thats 12% more dps
resto sham - personaly Id go ele though and off heal as needed unless u plan to 3 man instances

prot Warrior
demo loc - for mana efficency. though afli is more mana efficent imo it just doesnt work well in groups killing too slow.
druid - same as sham here Id go boomkin unless u plan to 3 man instances, just have a nice hot macro then swop to boomkin or just nuke.