Minor characters:
Mylune
Soulbinder Tuulani (would have liked a bit more stuff explaining what a soulpriest is, and where Draenei practices fit in with undeath and necromancy).
Major characters:
Lei Shen: I think he was one of the more interesting and better motivated villains, even though he himself had very little screen-time in WoW.
Lorewalker Cho: He really helped set up and sell Pandaria in terms of Lore. Also, his role in the Thunder King trailer can’t be overlooked (probably one of the best WoW patch trailers).
It’s hard to think of a third. There’s a lot of near misses, but they tend to fall into categories of “wish they’d done more” or “wish they’d been handled differently”.