Pretty old, but worth a re-post (if already posted), just so everybody is on the same page in regards to the changes to buff stacking. As it stands now, the following buffs within the same category will no longer stack:


# Armor Debuff (Major): Acid Spit (exotic Hunter pet), Expose Armor, Sunder Armor
# Armor Debuff (Minor): Faerie Fire, Sting (Hunter pet), Curse of Recklessness
# Physical Vulnerability Debuff: Blood Frenzy, (2nd Talent Spec TBA)
# Melee Haste Buff: Improved Icy Talons, Windfury Totem
# Melee Critical Strike Chance Buff: Leader of the Pack, Rampage
# Attack Power Buff (Flat Add): Battle Shout, Blessing of Might
# Attack Power Buff (Multiplier): Abomination's Might, Trueshot Aura, Unleashed Rage
# Ranged Attack Power Buff: Hunter's Mark (only Hunters benefit, so no need to exclude against other class abilities)
# Bleed Damage Increase Debuff: Mangle, Trauma
# Spell Haste Buff: Wrath of Air Totem
# Spell Critical Strike Chance Buff: Moonkin Aura, Elemental Oath
# Spell Critical Strike Chance Debuff: Improved Scorch, Winter's Chill
# Increased Spell Damage Taken Debuff: Ebon Plaguebringer, Earth and Moon, Curse of the Elements
# Increased Spell Power Buff: Focus Magic, Improved Divine Spirit, Flametongue Totem, Totem of Wrath, Demonic Pact
# Increased Spell Hit Chance Taken Debuff: Improved Faerie Fire, Misery
# Percentage Haste Increase (All Types): Improved Moonkin Aura, Swift Retribution
# Percentage Damage Increase: Ferocious Inspiration, Sanctified Retribution
# Critical Strike Chance Taken Debuff (All types): Heart of the Crusader, Totem of Wrath
# Melee Attack Speed Slow Debuff: Icy Touch, Infected Wounds, Judgements of the Just, Thunderclap
# Melee Hit Chance Reduction Debuff: Insect Swarm, Scorpid Sting
# Healing Debuff: Wound Poison, Aimed Shot, Mortal Strike, Furious Attacks
# Attack Power Debuff: Demoralizing Roar, Curse of Weakness, Demoralizing Shout
# Stat Multiplier Buff: Blessing of Kings
# Stat Add Buff: Mark of the Wild
# Agility and Strength Buff: Strength of Earth Totem, Horn of Winter
# Stamina Buff: Power Word: Fortitude
# Health Buff: Commanding Shout, Blood Pact
# Intellect Buff: Arcane Intellect, Fel Intelligence
# Spirit Buff: Divine Spirit, Fel Intelligence
# Damage Reduction Percentage Buff: Grace, Blessing of Sanctuary
# Percentage Increase Healing Received Buff: Tree of Life, Improved Devotion Aura
# Armor Increase Percentage Buff: Inspiration, Ancestral Healing
# Cast Speed Slow: Curse of Tongues, Slow, Mind-numbing Poison.