Also I always choose the most offensive dialog option I come across, joined both the DB and the TG and found quite a few occasions where I got the option of demanding of fellow travelers on the road that they hand over their possessions to me
So far, I haven't felt like the Dark Brotherhood or Thieve's Guild are particularly warm and fuzzy questlines.
Haha. But yeah seriously those are going to be your best bet . . . Would it really be realistic if 50% of the quests were 'good' and 50% 'evil'? Not really.
I almost wrote out some spoilers, but off the top of my head I came up with 3 solid evil (or at the very least villainous) things I've done through questing. Keep on truckin' around and opportunities will present themselves.
One quest comes to mind that has both evil and good resolutions, but I agree that there's a bias towards good. I'd be interested in a Mod or expansion that focused on evil play.