Willpower and Personality
Mage or Thief
Illusion (Mind Control Spells, Chameleon, Invisibility)
Sneak (Chamelon COMPLIMENTS not replaces this skill)
Conjuration (Not to sneaky, but lets something else fight for you)
Any Offensive Combat Skill (Face it, your eventually going to have some wet work)
Security OR Alteration
The remaining skills are to taste, I would avoid armor to get the most out of Illusion.
Sneak, Cast Frenzy on a group. Maybe toss out a monster with conjuration. Disappear. Repeat as Necessary until only one remanins alive. Send in a monster or use your offensive skill (Blade, Blunt, Marksman, Conjuration, Destruction, Hand to Hand) to clean up the last guy.
It's a fun playstyle IMO.