If you could have two classes at once...

[MrPistachio]

Badass wise, Deathknight and Warlock.

Immortal wise, Paladin and Druid. I'd be Resto Prot!

And damage wise, rogue and mage. It'd work somehow.

[BaseStamp]

paladin+paladin

[Chiruru]

Dk+Warrior

TG Frost!

[bruxx]

here are some ideas:
Warrior + Druid: Plate + 370% armour in dire bear form= ultimate tank even without talents
paladin + Deathknight: time to OP your ass off this world
Druid + huntard: what about sending your pet to tank an elite or something and you poof into a tree to heal it?
Warlock + shadow priest : talents can help ALL your spells
Rogue + Priest: just for the lolz

[Kaga]

Shaman hunter, like an elemental-physical ranged dps hybrid, with crazy heals and the capacity to fuck up anyone who enters your "dead zone"

Assuming the shaman half is all 3 specs right? :P

[mistuhbull]

Lock+Mage, I want Shadow Missiles damnit

Seriously though, Lock+Pally

[Sarrior]

You would still need a mh dagger to ambush...

In cata not anymore

Unholy DK + Destrolock

[Chieftain Hogger]

prot warrior + disc priest = protipline pririor
omg a tanking priest with 2 shields(bubble and normal) =)

[Ijanaak]

Shadow Priest and Warlock I guess... I like to press buttons and forget about it.

[trebor]

Spriest and affli lock... MOAR DOTS!

this, plus 15% more damage to the dots thanks to Shadowform

[Forblaze]

Warrior/Shaman - Titan's Grip + Windfury
Warrior/Hunter - Killstot, Intercept, Execute
Deathknight/Druid - HoT's, DoT's, Pets
Priest/Mage - PW:S, Divine Aegis, Ice Barrier, Mana Shield
and then i havent mentioned paladin yet

[Phobiosa]

Mage + Pally. Hearthstone on cooldown? No worries! Bubble+teleport!

[Deleted]

Mage+Pala. most powerful spells, plate, bubble, dispel, 2hander LOL

[Lazertrooper]

frost mage + disc priest, best combination and synergy of gear.

[NisseFrasse]

I would go for Warlock and Warrior. Go into melee with either two big weapons, or a twohanded, along with my demon at my side! Not sure if I would be Destru of Demo, hmm. Or as for Warrior, Fury or Arms. But there is allready a Warlock Warrior guy! Grand Warlock Nethekurse! He got a Bladestorm with Deathcoils! Thats damn awezome! Warlock and Warrior, my two favorite classes, mhm~!

[Honkeymagoo]

Prot Paladin/ MM Hunter

Double all paladin and hunter cds with readniness

You'd be able to kite endlessly while maintaining really good dps. If you did get damaged then you could reset the battle so many times that you'd probably be able survive until all your cds were up again and repeat this endlessly.

[Spl4sh3r]

Hunter + Druid ofcourse :P

Two stealthing cats coming at you from nowhere

[nonshallpass]

mage with a priest or pally
grrrr unkillable

[Lazertrooper]

People choosing classes with different armour class and stat requirements are just retarded tbh.

[Arcanimus]

Hunter/Druid obv, stealthed cat with a tamed druid pet, self healing, starfall, typhoon, trees, oh, and ZOMGWTFBOOMKINSHOOTINGMEWITHAGUN