Also note that power leveling is sometimes used to refer to paying someone else to level your character to cap as fast as possible (i.e. they power level for you); a distinction used by Blizzard is to refer to the paid leveling as "power leveling service." This behavior is against Blizzard's Terms of Service. Power leveling yourself, which this article covers, is perfectly acceptable.
Affliction: Endless Affliction - Your Unstable Affliction deals the same damage as normal, but its duration is increased by 6 sec. Demonology: Nether Ward - Surrounds the caster with a shield that lasts 3 sec, reflecting all harmful spells cast on you. Destruction: Demon Armor - Protects the caster, increasing maximum health by 10% and increases armor by 150%. Warrior
Heirlooms are special pieces of armor that level up with your character, so they have stats that are always respectable for your character’s level (up to level 110). Heirlooms that fit the head, shoulder, chest, legs, and back armor slot offer an experience bonus. The total bonus is 45 percent if you have them all. It’s also possible to acquire a ring that adds another 5 percent, but you must win a fishing contest acquire it, and that can take some time.