Shamelessly reposted... copied and saved from another's post.
Different buff types and their bonuses.
Buffs from the same group do not stack, you get the best of the set.



BUFF TYPES

280 Spell Power -> Elemental Shaman -> Totem of Wrath (Fire)
10% of Casters Spell Power -> Demo Warlock -> Demonic Pact
144 Spell Power -> All Shaman -> Flametongue Totem (Fire)


13% Spell Damage -> Affliction Warlock -> Curse of Elements
13% Spell Damage -> Balance Druid -> Earth and Moon
13% Spell Damage -> Unholy DK -> Ebon Plaguebringer


5% Haste -> All Shaman -> Wrath of Air Totem (Air)
3% Spell Haste -> Balance Druid -> Improved Moonkin Form
3% Haste -> Ret Paly -> Swift Retribution


5% Chance to be Crit (debuff on boss) -> Frost Mage -> Winters Chill
5% Chance to be Crit (debuff on boss) -> Fire Mage -> Improved Scorch
5% Chance to be Crit (debuff on boss) -> Destro Warlock -> Improved Shadow Bolt


5% Crit -> Elemental Shaman -> Elemental Oath
5% Crit -> Balance Druid -> Moonkin Aura


3% Hit -> Shadow Priest -> Misery
3% Hit -> Balance Druid -> Imp Faerie Fire


3% Damage -> Beast Mastery Hunter -> Ferocious Inspiration
3% Damage -> Ret Paly -> Sanctified Retribution


10% to all Stats -> All Paly -> Blessing of Kings/Sanctuary


750 Armor, +37 all Stats +54 Resists -> All Druid -> Mark of the Wild


80 Spirit -> All Priest -> Divine Spirit
64 Spirit -> Warlock with Fel hunter -> Fel Intelligence


60 Intelligence -> All Mage -> Arcane Intellect
48 Intelligence -> Warlock with Fel hunter -> Fel Intelligence


91 MP5 -> All Paly -> Blessing of Wisdom
91 MP5 -> All Shaman -> Mana Spring Totem (Water)
109 MP5 -> Resto Shaman ->Improved Mana Spring Totel (Water)


30% Haste for 40 Seconds -> All Shaman -> Bloodlust/Heroism