My (not yet 70) team has a pally tanking for four shamans. I'm very happy with the choice to use a pally rather than a druid or warrior.

1. Amazing AoE tanking
2. Better buffs (BoK/BoW/JoW)
3. Magic is (overall) more dangerous than curses, so cleanse > decurse.
4. You can heal one of your minions in a pinch, without losing all your defensive power like a druid would.
5. Ranged taunt (not as necessary as everyone says, but still good)
6. Ridiculously easy to get and hold aggro in general

I feel like pallies, in general, are the best tanks for 5-man content, which is what you're going to tank as a multiboxer anyway.