Alchemy, marksman, and mysticism. I've always had alchemy; it's dead useful. With it, I don't have to worry about buying healing potions. And it's a good way to make a little extra money.
For marksman, what can I say? It's fun to shoot cliffracers from a distance.
And as for mysticism, well, I can zap away from danger, or if I have a bunch of crap to sell. And soul gems. What else?