My favourite would be one where when performed you leap high into the air (up to about 10-15 meters), and glide back down on the winds, controlling your speed and direction. This would allow you to glide long distances if you jump off a mountain peak, or simply leap up onto a high ledge, without being a bit too overpowered by being able to reach places that you're not intended to reach right away. It would make sense too, because the whole idea around the dragonshouts is that they're carried in the wind.
I'd also like to see a flamethrower-like "dragon breath". It would also be nice if there were different dragons that you could call down. For example, for larger a larger enemy or boss you could call down a single very powerful dragon, but if there's a whole bunch of weaker enemies that are swarming you, you could call down a mother and her dragonlings as a kind of "crowd control".
Udig? Any ideas?