M'lord Sheogorath endorses this one. He and Majin Boo should team up and make a "cheese morph" spell
You win simply for making a Majin Buu Reference lol DBZ FOR LIFE!...Could you imagine a combo between Buu and the Mad God...WOW...now that would be interesting lol.
BACK ON TOPIC!
A possession shout, as mentioned above would be AWESOME so would the badass vortex (although it is a little, Avatar the Last Airbender to me haha) the problem with the possession one is that it may screw up the faction system and codes of the possessed after you leave them. Unless you mean more like a mind control thing in which you take over their mind and can make them follow you or trade things with you or whatever. ooo that's a good idea
MIND CONTROL!

You shout and your victim's will is bent to your own. You can make them follow you, or even take from their inventory. You can possess 3 people at once (one person per word) and it should have a very long cool-down time.
Mirage: Make 6 identical dragonborn illusions (2 per word) that confuse enemies making them attack them, leaving them open to your attacks (it could work cause one of the Gaulderson bosses uses it)
Dragon Rage: Dragonborn (1st word) takes 20% less damage but deals 10% more, (2nd word) Dragonborn Takes 50% less damage but deals 25% more (3rd word) Dragonborn takes 80% less damage but deals 40% more (the problem I foresee with this is when mixed with Orc beserking it could make the player WAY too powerful.
ummm I'm out for now haha.