According to Ghostcrawler on the Cataclysm Beta forums, here are the class synergy thoughts for Cataclysm as of today:

Balance druids will be providing spell haste and spell damage increases.
Agility and Strength – Death Knight, Shaman, Warrior
Armor – Shaman, Paladin
10% AP – Marksmanship Hunter, Enhancement Shaman, Blood Death Knight, Paladin
Burst Haste – Shaman, Mage
3% Damage – Beast Mastery Hunter, Arcane Mage, Retribution Paladin
Health – Warlock (probably Destruction), Warrior, Priest
Mana Pool – Mage, Warlock (probably Affliction)
Mana Regen — Paladin, Shaman, Warlock (probably Affliction)
Replenishment — Shadow Priest, Frost Mage, Survival Hunter, Destruction Warlock, Retribution Paladin
5% Crit — Fury Warrior, Feral Druid, Subtlety Rogue, Elemental Shaman
20% Melee Attack Speed — Shaman, Frost Death Knight, Retribution Paladin, Survival Hunter
5% Spell Haste — Shaman, Balance Druid, Shadow Priest, Destro Warlock
6% Spell Power — Mage, Shaman
10% Spell Power — Elemental Shaman, Demonology Warlock, Fire Mage
5% Stats — Paladin, Druid

12% Armor Debuff — Warrior, Rogue, Druid, Hunter
10% Physical Damage Debuff — Warrior, Druid (probably bear), Protection Paladin, Warlock, Blood Death Knight
30% Bleed Damage Debuff — Arms Warrior, Feral Druid, Subtlety Rogue
30% Cast Speed Slow — Warlock, Rogue, Arcane Mage
5% Spell Crit Chance Taken — Fire Mage, Warlock (probably Demonology), Mage (possibly Frost)
25% Healing Taken — Arms Warrior, Fury Warrior, Hunter, Rogue, Frost Mage, Shadow Priest
10% Melee Attack Speed Debuff — Warrior, Death Knight, Feral Druid, Protection Paladin
4% Physical Vulnerability — Arms Warrior, Combat Rogue, Frost Death Knight
8% Spell Damage Taken — Warlock, Unholy Death Knight, Balance Druid, Assassination Rogue

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