Conjuration and You: How two Dremora Lords could beat the shit out of Dovakhiin if they ever wised up and turned on me. It's kinda boring, but it absolutely decimates master difficulty.
2 dremora lords, shield user (usually an equipped lydia) merc, and i've got the assassin summon power and the sovngarde hero shout if it's ever really required.
Also, if the dragon won't come down and you don't have dragonrend yet, you can usually just use 2 storm atronach thralls who will blast the bastard outta the sky <_<
edit: Oh, and sometimes with blocking there would be a bug with the slow-time perk...it'd slow the game down (not you, just everything else) and you could literally just walk through a dungeon slapping everything in the back, nothing fighting back. Interesting but boring bug in the end. I guess Skyrim's like the other TES, though, you gotta find your own challenge and using game mechanics -too- well will invariably make the game boring. MMO min-maxing is tough to stop