Blizzard wont change the way 10 man instances work in WotLK, so here is my lineup.
(seems I actually missed more changes than I thought since I stopped playing in March. See the post below for corrections, It's really helpful)
Feral/Prot-Pala/Def-Warrior/DK--------------Maintank
Resto Druid--------------------------------Healer (Imp. ToL Aura)
Hunter (Survival/BM)-----------------------DPS (Surv: Hunting Party! <-imba)
Deathknight/Fury/Ret.Pala------------------DPS (DK OT)
Melee-Shammy/Rogue/Feral (cat)-----------DPS (Feral OT)
Moonkin-----------------------------------DPS (Aura)
Ele.Shammy-------------------------------DPS (Totem)
Mage/Shadowpriest------------------------DPS (Mana-Battery/Int,Food)
Warlock (Destro/DoT)----------------------DPS (no love for gayguards)
Holy-Priest/Resto-Shammy-----------------Healer (G-Spirit,CoH vs. Spirit Link&Earth-Shield)
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Explanation
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Maintank:
Any Tank with decent def. gear and def. spec will do. Take what you get and stick to it.
If you decide to take a Fuzzy Wuzzy Feral look to it that he also has decent cat dps gear
for some encounters might be like Shade of Aran and Netherspite. The other tank classes don't need extra dps gear, their spec wont allow them to deal damage.
Healers:
Resto Druid is not an absolute "must-have" but definitely the best class/spec for the slot in the tank/melee group because they will need more healing than the ranged group and Improved ToL Aura would give you ca. 300 +Heal with level 70 gear. Imagine what it will be when you hit 80 and get T7.
Holy-Priests and Resto-Shammy are both pretty imba. I prefer the priests tough. They really have ALL the tools to get the job done.
DPS Grp1:
Let's make this short. Survivals are elite. Period. In WotLK you can drink only ONE potion per fight. So Hunting Party gives Grp1 all the synergies they need. +2% Mana, +10 energy, +10 runic power and +4 rage EXTRA EVERY 8 SECONDS. You can't beat that. Beastmasters are "ok" ... but as always pretty much self-serving (No synergies except miserly 3% +dmg). Marksman are a No-No!
Melees are a bit tricky. You have to choose between Bashor Shammy and Kitty (Windfury&AP or Crit&Heal) because Cats don't profit from windfury you should not force them into the same group. Just think of the other melee classes. It would not be fair for Fury/Retri/DKs and Rogues to NOT get into the group at all because their slots are taken by two classes who are unable to use ALL their synergies.
DPS Grp2:
Let's make this short again. Moonkins got too much love in WotLK, it's like all the devs where on extacy. But that's a good thing, every spec should have their moment of glory. In BC all they got was spatter in the face. Now one just wants to hug them and never let go again. Here is why:
+20%! spell haste every 30 seconds
+3% Chance to hit for all Melees, Casters and Ranged DPS
+5% Spellcrit for your party
+6% Nature and arcane DMG for everyone
+they still have Tranquility for that WTF-emergency-group heal situations, no other caster dps class can do something like that
+they still have rebirth, no other caster dps class can do something like that
Nuff said.
Ele Shammy:
-6% Mana costs by spells and abilities for your party
+6% all critical strike damage for your party
+3% Spell Crit
+3% Spell Hit
For the Shadowpriest/Mage and the DoT-Lock/Destro-Lock decision I really can't say much. They all profit from one another in some way. But I think Shadowpriest + DoT-Lock or Firemage + Firedestro would get the most of it.
The End.
(No love for (*cough*) Bacon-Palas though.)