Applejack - Prot/Ret Paladin with herbalism and cooking.
Fluttershy - Resto/Feral Druid.
Pinkie Pie - Mage or Rogue, since she can pop out of nowhere!
Rainbow Dash - Engineering for speed boosts. Shaman or Balance Druid for her way with the weather.
Rarity - Tailoring and Jewelcrafting (duh). Priest, maybe?
Twilight - Warlock with inscription, only she'd have a baby dragon familiar instead of a demon.

Seriously guys, I'm gonna hork.

An important question that deserves a good answer.

Twilight Sparkle - Arcane mage. she's the magic user, pretty easy.
Applejack - Arms Warrior. She's all about the brute strength.
Rainbow Dash - Oh god. Uh...Ferals run the fastest. This is harder than I thought it'd be.
Fluttershy - Holy priest in personality, hunter in terms of skills.
Pinkie Pie - boomkins are silly, right? No real clue here.
Rarity - Holy pally. She loves helping people out and she spends hours on her hair. Easiest one.

Darn you guys...I think it's time for a warcraft(s) project.

Defiantly agree that Applejack is a plate-wearing melee class, warrior's probably the best fit.

I find Rarity kind of annoying, but she's clearly a caster, so Belf Warlock (agree with JC/tailoring, no brainer)

Fluttershy seems resto druid-ish. But ANGRY!Fluttershy seems more BM hunter ish

Twilight's an arcane mage, straight up. Inscription and alchemy, maybe?

Rainbow Dash has the whole weather/element connection of a shammy, but that feels a little... immobile for her.

Pinkie Pie? No clue. She would take engineering for the toys and barely-controlled craziness, but she doesn't match up with any class as far as I can tell. She can be a Pandaren Bard. Because it's Pinkie Pie

Seriously, I love you guys :)

Just in case anyone needed inspiration to customize a My Little Pony to look like a WoW toon....

http://ohnotheydidnt.livejournal.com/33538342.html?page=2&cut_expand=1#cutid1

My friend has a pony for every class.

Pinkie Pie - Hunter (for Gummy), engineering for the roflcopter
Fluttershy - Druid ("I would like to be a tree")
Rainbow Dash - Rogue (duh)
Twilight Sparkle - Mage
Rarity - Priest (dunno)
Applejack - Warrior
Zekora - Shaman
Celestia - Paladin
Nightmare Moon - DK
Trixie - Warlock

She's also got professions figured out for each but I can't remember most of them.

Don't say I didn't warn you.

http://www.youtube.com/watch?v=9S7kg1IhZ7M

The ponies will group up to defeat My Little Lich King:
http://mugi-hamster.deviantart.com/art/My-Little-Lich-King-209586801

Applejack, hero of Ponyville for saving the town from a cow stampede, is clearly a Beastmastery Hunter.

Rainbow Dash is the plate-wearer (see her ideal outfit in "Suited for Success" if you have any doubt).

Twilight is obviously a Mage, with Inscription, Enchanting, and a high-level Archeologist.

Apple Jack is a Prot Warrior with Herbalism and Mining.

Rainbow Dash is a Kitty Druid, no known professions, but to be round, I'll call Jewelcrafting and Leatherworking

Fluttershy is a Resto Druid, probably with Herbalism and a very large pet collection.

Pinkie is a Beast Mastery Hunter, with an Crocolisk Pet, tailoring and Engineering.

Rarity is a Warlock, with Tailoring and Jewel-crafting.

*main
wait...
o i c what you did there

Oh god. A Pony fandom within the WoW community.....a BIG one.....

*feigns death*

I gotta say I like different parts of the different lists here.

Applejack I see as a Warrior. I'd say herbalism is a safe skill to give her. And maxed out cooking.
Twilight Sparkle seems like a Mage to me with Enchanting and Inscription Archaeology maxed sound like a dead ringer.
Rarity would be a Priest, she's already "wearing" a Priestly white, and she loves to help others, but make her mad and that Shadow off spec comes out as she says "It Is ON". Tailoring and Jewel Crafting are what she actually does in the show! No choice there really lol.
Fluttershy has already said she'd like to be a tree, so would many Resto Druids. I would give her Feral off spec, cause when she's pushed to her limits she's like a Bear tank! It's hard to say what professions she'd have, but she would have a crap ton of vanity pets.
Rainbow Dash, there are a ton of classes she'd fit. I'd almost go as far as to say she'd be every class. Her competitive nature would bush her to be the best at everything, at least one of each class max leveled, all of them with engineering for those sick speed boots and awesome gadgets to ensure that she gets ahead at everything. Her maine though would probably be a Rouge.
Pinkie Pie I'd place as Hunter for the same reasons as most of the above. She'd use that camouflage ability Hunters have to POP up out of anywhere, she'd have a crocoslic pet, and Engineering for the roflcopter is just win.

I can't believe that nobody has said that Fluttershy has to have Tailoring. It was only with her scary knowledge of sewing that they were able to finish Rarity's outfit after all.

I'm going to have to agree with eakin3, and the more I think about it, I think BM Hunter really fits Fluttershy, because they can be really quiet, but also bring the noise when they need to. Definitely has to have the Littlest Pet Shop achievement.

I see Twilight Sparkle as an Arcane Mage (the mage most dedicated to pure unadulterated magic), Applejack as a Protection Warrior (strong, reliable, protective of her friends), Rainbow Dash as a Retribution Paladin (20% cooler than the other specs), Rarity as a Discipline Priest (generously clothing her targets in protective bubbles), Fluttershy as a Resto Druid (she has to be a healer, and druids love animals), and Pinkie Pie as an Elemental Shaman (no class relies on feelings and communication quite like a shaman, and Pinkie's gotta blow things up).

Of course, the reason I feel this way is because I have been reading this: http://www.equestriadaily.com/2011/06/story-world-of-ponycraft.html