I've really enjoyed:
- 5x Feral and 5x Resto Druids (same team).
- 4x Death Knights + 1x Paladin (Heals).



When I was doing a PvE team, my favorite was:
- Prot Paladin, Demo/Destro Lock, 3x Shaman (2x Elemental, 1x Elemental & Resto dual-spec).

My current PvE teams (just leveling them, not doing heroics) are:
- Blood DK, Holy Priest, Arcane Mage, Destro Lock, Elemental Shaman.
- Boomkin/Feral Druid, 3x Elemental Shaman, 1x Elemental/Resto (dual-spec) Shaman.



It looks like Warlocks and Ret Pallies will be amazing in the expansion.
Not sure if you want to have a set of either available on one faction or both.