My mage is evil to the core so he should be casting dangerous and forbidden magics like shadow magic.
There was a spell called "Sphere of Negation" in Daggerfall, which might please you then. Maybe they'll reintroduce it?
Also, I just thought to something...
What if the Dawn was actually "what repels the Shadows"? Maybe we'll have to fight against a Shadowmage in Dawnguard? After all, the last Umbra' Keth lived in the Crypt of Hearts, of which an entrance was located in Skyrim, so it wouldn't be that much astonishing...
Yet another speculative theory about dawnguard...
I need new information!

I am really looking forward for the E3...