Dont forget all the Death Knighest shouts - Dismay, ice form, frost brealth, ethereal, maybe slow time, call dragon (if playing on the computer and play with a mod that only calls undead dragons), and the new one coming with the DLC.
Check out Ghostblade; at negligible weight, it's the fastest weapon there is. Minimal stamina use. 3 ectoplasms to upgrade.
Get the dark elf assassin chick in Whiterun as a follower when you get the Dark brotherhood suit. Your own personal assassin/bodyguard bought and paid for.
Dead Thrall...a bad ass Orc follower with pimped out orcish armor. With magic item slots - fortify stamina and health, fortify heavy armor. And a wizard thrall or vamp.
And Ritual Stone.