There are currently 12 level 80 heroics in the game and 11 of them have been cleared by the following setups:

Pally Tank, Resto Shaman, 2 Elemental Shaman and Balance Druid
Pally Tank and 4 Elemental Shaman

This is just what I know about, there may be others.

I personally run Pally Tank, Resto Shaman and 3 Elemental Shaman and have cleared 5 heroics by myself.

Unlike Multilocks, I read the patch notes differant and think the changes only apply to vehicle mounts, not all vehicles, making the 12th heroic almost if not entirely impossible.

As for your group, pally tank is probably the easiest but death knights are definately gaining favor and for your casters I would probably go healer (I don't think it really matters which but shaman are pretty easy as they basically have two heals), 2 elemental shaman and a balance druid. I personally don't have a balance druid because I don't feel like going back and leveling one but they currently bring better buffs/debuffs than a 3rd elemental shaman does especially if your healer is already a shaman.