If "you could buff any class -- any class but your own (your main or mains if you've got multiple) -- which class would it be and how would you buff them?"
I'll say that if you want cool points on this one, you should stay away from any classes you play regularly-- for me at the moment, that'll be shaman, rogue, and hunter. I really like anti's answer of priests-- they are QQing a lot, but there is no reason they should be DPSing while paladins heal in raids.
Personally, I'd hook up prot warriors a little bit-- right now, their DPS is such a joke that the only way they can really play is in instances. I'm not saying that we should give them tons of DPS-- that would mess everything up in PvP-- but just a little extra DPS would let them solo, and wouldn't unbalance PvE groups that much (since it's likely that if the group makeup is right, the prot warrior's DPS will still pale in comparison to your regular DPS class's hits).
A buff like that isn't really necessary, but it's an interesting thought experiment to see where you might make positive changes that don't actually affect you. So if Blizzard suddenly gave you the chance to buff any class except your own, what would you say?