1) War of the Three Clans
Dress up as a Wildhammer and help defeat the Dark Iron dwarves. Run like hell when you see the summoning of Ragnaros and most of the Redridge Mountains explode.
2) First Troll War against Hakkar
It's like ZG, but... not ZG. Maybe it's ZG but with about ten million trolls fighting with you and against you.
3) Scarlet Crusade vs. the Scourge
Somewhere I want to take part in a giant battle with the Scourge, but do it from the side of an enemy.
What do you want to see and take part in?