To my mind, most of the tamable creatures up there would be icier versions of pets we already have, which are native to Azeroth. Outland had so much more potential in terms of new and exotic pets, yet Blizzard only gave us a few new types, then went and left most of them without any appreciable abilities. Why would anyone tame a spore bat, or a nether ray, when neither of them can train in certain necessary abilities? Why enable these pets if taming them would be so useless? Some people love the dragonhawk, but the only pet from outland everyone agrees was a popular success is the ravager, though it's a bit ugly for my tastes.
So, because it's fun to daydream and speculate, lets imagine what sorts of new pets we'll get to enjoy in Northrend! This means not just wolves and bears with extra spiky icicles or something -- truly new pets we've never seen before. Can you come up with something particularly icy?