Wow many thanks for the replies. That's really interesting about your actions affecting your random encounters... I always seem to encounter inept mages looking to practice wards with me or in possession of a staff of zombies with my mage character. I'll look into these necromancer suggestions.
But any other kinds of evil to root out? I realise how odd my question is and how annoying I must be getting by now (sorry!) but I really love this mage character and I want to keep playing her. I'm not going to stop roleplaying (so no companions TG DB lol) so I really need evil sorcerors, necromancers, generally bad people to slay!
Thalmor. KIll the Thalmor in the wilderness, take their valuable loot, and leave their bodies to the elements. The Thalmor are about as evil as you can get. The comparisons to the SS are not without merit.
That said, the Companions might not be a bad way to go, except that you're a mage and not a warrior-type.
There are quite a few draugr dungeons around - those are always good, and if you have good Restoration skills you can focus on combatting the undead. Vampires will show up if they haven't already, and there's one minor quest revolving around vampires at least.
Hell, if you wanna rid the world of some kind of evil, try and hunt down the DB and kill as many of them as you can. Ditto for the thieves' guild; they're turning Riften into a corrupt city.