I wear master robes, the dragon priest mask that gives 100% extra mana regen, the dark brotherhood boots and gloves (light armor), the boots have a muffle enchantment, and the gloves give you double sneak damage with one-handed weapons, so with the assassins blade perk, my ebony dagger does 30x sneak damage! (no high sneak skill required)
On one hand i have my ebony dagger, on the other the expert level illusion spel: invisibility. Using the db boots enemies cant hear me, and thanks to the invisibility they cant see me, making it impossible for them to detect me, this way you can even stealth-assassinate dragons!
The invisibility spell does wear off when you kill someone, so it's wise to either train your illusion, or have a large amount of mana.