Priest - Easy leveling 31+

Basicly something we found out entertaining with a friend and so far it has been great success on my Priest upto lvl 73 at the moment.

Basicly you will need this spec if you are lvl 31: Talent Calculator - World of Warcraft after that it is upto you where you spend your points at.

The key talent points in this case are 2/2 Atonement which makes your Holy Fire (including the dot) and Smite heal the lowest health party member for 100% of the damage they deal.
Also you will want to pick up the glyph Divine Accuracy for automatic hit cap for both these spells.

Later on you will want to pick up Divine Aegis because the heals are always critical when your spells are thus making this talent very useful.

This makes it EXTREMELY easy & fast to level up in instances. You cant basicly oom with Holy Fire/Smite spam + it heals way more than any encounter has dealt damage so far upto lvl 73. 
(Smite heals for more than Heal + costs almost the same mana)

Have fun leveling, atleast we are having loads of fun like this 

Dont know how long this lasts but I reckon it is good for anything before the Cata dungeons atleast!