They use to scare the hell out of me too, mostly because if I saw them that meant either death or a lot of running away.
Then I just built up destruction and grabbed a higher level fire spell now I can take them out with one swift cast of Incinerate.
One time three jumped out at once and it took me all of four seconds to kill them.

Just so y'all know for future playthroughs.... the frost troll on the way up the 7000 steps can be got around - when you get just before the narrow declivity where it spawns, hike to the left around the knoll - there's a fairly easy way to get around, and when you come back to the steps you'll be far enough beyond the troll that you won't ever see it.

Invisibility spell, sneak and a Daedric bow. Boom head shot!

Of course this is at level 50. At earlier levels I survived by basically sneaking across Skyrim. I kid you not.

I dual-wield fully perked conjured swords against them. Just took out three Frost Bears(all at once) that way the other day.
If you've got the spell, flame atronachs are pretty effective. Even if they get swiped, they'll leave a nice fiery explosion that will do major damage. Also, it one nordic dungeon (can't remember which, I'm sure someone else will) you'll find one lady trying to get through(beware, there is a dragon priest at the end). If you help her, she'll give you the "Flaming Familiar" spell tome. This summons a kamikaze flaming spirit wolf that explodes in fire when it finds its target. Very effective if the fire wolf can reach the troll before exploding. It also doesn't cost that much to cast if you've been paying attention to you magic when leveling up.

Edit: Werewolves are pretty effective as well. I use Beast Form against Giants and I can usually get them off their feet long enough to get swiped to death.

This. 4 fireballs and dead.