T13 Set Bonus (Subject to change)

[Milli]

Death Knight

    Blood, 2P -- When an attack drops your health below 35%, one of your Blood Runes will immediately activate and convert into a Death Rune for the next 20 sec. This effect cannot occur more than once every 45 sec.
    Blood, 4P -- Your Vampiric Blood ability also affects all party and raid members for 50% of the effect it has on you.
    DPS, 2P -- Sudden Doom has a 30% chance and Rime has a 60% chance to grant 2 charges when triggered instead of 1.
    DPS, 4P -- Runic Empowerment has a 25% chance and Runic Corruption has a 40% chance to also grant 710 mastery rating for 12 sec when activated.


Druid

    Balance, 2P -- Insect Swarm increases all damage done by your Starfire, Starsurge, and Wrath spells against that target by 3%.
    Balance, 4P -- Starsurge generates 100% extra Lunar or Solar energy while Eclipse is not active.
    Feral, 2P -- While Berserk is active, Savage Defense absorbs are 100% larger, and your Blood in the Water talent now causes Ferocious Bite to refresh the duration of your Rip on targets with 60% or less health.
    Feral, 4P -- Frenzied Regeneration also affects all raid and party members, and your Stampede talent now grants two charges after using Feral Charge (Cat).
    Restoration, 2P -- After using Innervate, the mana cost of your healing spells is reduced by 25% for 15 sec.
    Restoration, 4P -- Your Rejuvenation and Regrowth spells have a 10% chance to Timeslip and have double the normal duration.


Hunter

    2P -- Steady Shot and Cobra Shot generate double the amount of focus.
    4P -- Your Arcane Shot ability has a chance to grant 25% haste to you and your pet for 10 sec.


Mage

    2P -- Your damaging spells have a 30% chance to grant Stolen Time, increasing your haste rating by 50 for 30 sec and stacking up to 10 times. When Arcane Power, Combustion, or Icy Veins expires, all stacks of Stolen Time are lost.
    4P -- Each stack of Stolen Time also reduces the cooldown of Arcane Power by 3 sec, Combustion by 4 sec, and Icy Veins by 6 sec.


Paladin

    Holy, 2P -- After using Divine Favor, the mana cost of your healing spells is reduced by 25% for 15 sec.
    Holy, 4P -- Increases the healing done by your Holy Radiance spell by 20%.
    Protection, 2P -- Your Judgement ability now also grants a physical absorb shield equal to 30% of the damage it dealt.
    Protection, 4P -- Reduces the cooldown of Divine Guardian by 60 sec and increases the radius of its effect by 70 yards.
    Retribution, 2P -- Your Judgement ability has a 50% chance to generate 1 Holy Power.
    Retribution, 4P -- While Zealotry is active your abilities deal 12% more damage.


Priest

    Healer, 2P -- After using Power Infusion or Lightwell, the mana cost of your healing spells is reduced by 25% for [10|15] sec. (10 sec for Discipline, 15 for non--Discipline.)
    Healer, 4P -- Your Power Word: Shield has a 10% chance to absorb 100% additional damage, and the cooldown of your Holy Word abilities is reduced by 20%.
    Shadow, 2P -- Shadow Word: Death deals an additional 55% damage, and you no longer take damage from your own Shadow Word: Death when the target fails to die.
    Shadow, 4P -- Your Shadowfiend and Shadowy Apparitions have a 100% chance to grant you 3 Shadow Orbs each time they deal damage.


Rogue

    2P -- After triggering Tricks of the Trade, your abilities cost 20% less energy for 6 sec.
    4P -- Increases the duration of Shadow Dance by 2 sec, Adrenaline Rush by 3 sec, and Vendetta by 9 sec.


Shaman

    Elemental, 2P -- Elemental Mastery also grants you 400 mastery rating 15 sec.
    Elemental, 4P -- Each time Elemental Overload triggers, you gain 200 haste rating for 4 sec, stacking up to 3 times.
    Enhancement, 2P -- While you have any stacks of Maelstrom Weapon, your Lightning Bolt, Chain Lightning, and healing spells deal 20% more healing or damage.
    Enhancement, 4P -- Your Feral Spirits have a 45% chance to grant you a charge of Maelstrom Weapon each time they deal damage.
    Restoration, 2P -- After using Mana Tide Totem, the cost of your healing spells are reduced by 25% for 15 sec.
    Restoration, 4P -- Increases the duration of Spiritwalker's Grace by 5 sec, and you gain 30% haste while Spiritwalker's grace is active.


Warlock

    2P -- The duration of your Doomguard and Infernal summons is increased by [15|45] sec and the cooldown of of those spells is reduced by 4 min. (45 for Demonology, 15 for non--Demonology.)
    4P -- Soulburn grants a 10% increase to your spell power for 10 sec.


Warrior

    Protection, 2P -- Your Revenge ability now also grants a physical absorption shield equal to 20% of the damage done by Revenge.
    Protection, 4P -- Your Shield Wall ability now grants 50% of its effect to all party and raid members.
    DPS, 2P -- Heroic Strike costs 10 less rage while Inner Rage is active.
    DPS, 4P -- Your Execute critical strikes have a 20% chance to refresh the duration of Colossus Smash.


Courteousy of MMO Champion - all sets are Pre-PTR but gives you an idea of what they are thinking about

[Shadowsong]

I think those set-bonusses (spelling) aren't likely to go live.
Because if it's like this, some classes got very powerfull bonusses, while others hardly get something worth mentioning as "bonus".

For example, looking at the warlock set and it's supposed bonus.
Doomguard and Infernal are nice DPS boosts, but usualy you only use those on boss encounters and not on trash (at least not in 5 man dungeons, can't say about raids because I haven't done those). So meaning the 2 setbonus is kinda useless most of the time.
Also, looking at bonusses in previous warlock sets, it usualy boosts damage straight away on abilities you use a lot (dot's like immo, unstable affli, or busts like incinerate, chaos or shadowbolt).

[Jesung]

I think those set-bonusses (spelling) aren't likely to go live.
Because if it's like this, some classes got very powerfull bonusses, while others hardly get something worth mentioning as "bonus".

For example, looking at the warlock set and it's supposed bonus.
Doomguard and Infernal are nice DPS boosts, but usualy you only use those on boss encounters and not on trash (at least not in 5 man dungeons, can't say about raids because I haven't done those). So meaning the 2 setbonus is kinda useless most of the time.
Also, looking at bonusses in previous warlock sets, it usualy boosts damage straight away on abilities you use a lot (dot's like immo, unstable affli, or busts like incinerate, chaos or shadowbolt).

Trust me Shadow this one of the best 2 set Bonuses we have ever had. The CD on DG atm is stupid at 10 mins, so reducing that to 6 is an absolute god-send, especially for Demonology Warlocks as it is such a huge DPS increase. The previous Doomguard, realistically could not be used on every attempt of a progression fight unless you waited for it to go off CD for about 3 mins.

This will also allow it to be used in longer fights akin to Alysrazor which lasts for 11+ mins. Also about it being useless most of the time, people who *need* the 2 piece are raiders an thus need it on bosses more than anything, and is not needed on trash or 5 mans.

[Azunai]

Prot warrior ones are pretty OP, or depending on how you look at it, the DPS warrior ones are pretty Underpowered.

Heroic strike isn't really your prime DPS, not even with Inner Rage up (once a minute for 10 seconds iirc), and 20 Rage is still pretty steep for its damage.  
The 4p is only really beneficial for Fury. As arms you're proccing Colossus smash anyway and you're still doing rotation sub 20% so not just spamming Execute. Even in Fury it's very situational: Has to be sub 20% hp, has to crit, and then there's a 20% chance. =\

I reckon it'll be changed, yes ;-)

[Grimnar]

The 2p for a feral dps/tank is just crap.........
The 4p tanking side can be usefull as a sort of second tranq. but for a feral dps it is crap....


Blizz hasn't learned a thing about ferals i guess as at the moment we have crap 2p/4p bonus and it seems we continue on that path...

[Twyst]

Death Knight

    Blood, 2P -- When an attack drops your health below 35%, one of your Blood Runes will immediately activate and convert into a Death Rune for the next 20 sec. This effect cannot occur more than once every 45 sec.
    Blood, 4P -- Your Vampiric Blood ability also affects all party and raid members for 50% of the effect it has on you.
    DPS, 2P -- Sudden Doom has a 30% chance and Rime has a 60% chance to grant 2 charges when triggered instead of 1.
    DPS, 4P -- Runic Empowerment has a 25% chance and Runic Corruption has a 40% chance to also grant 710 mastery rating for 12 sec when activated.

Blood 2P bonus sounds "meh". It *could* enable another DS, but it also could not as DS requires 2 runes.
Blood 4P will get nerfed. The sounds waaay OP seeing as VB is popped almost every 60 seconds. OK, I don't use it right off CD as I save it for when I know a medium sized hit is incoming but this would make me use i a lot more I guess. But then again maybe it will stay because the DK is the only tank without a raid wall.

DPS 2P is awesome for unholy. That's a massive DPS boost as we can super-size Timmy faster. (arena PvP has 2/3 SD as opposed to the normal raid PVE 3/3 SD)
Death Coil is unholys hardest hitter.
It's quite lackluster for frost if it's an arena based spec as we don't tend to spec Rime at all.
DPS 4P on the other hand is "nice" for Frost as it benefits more from Mastery than unholy.

[Sharpfang]

woop woop, 4p prot warrior one looks grreat!