Restoration loop + Roggvir's Amulet of Talos = unlimited shouting with no cool down period so long as amulet is not unequipped. Player level 17, no armor, alchemy 100. M 100, H 100, S 260. It's actually pretty fun.
Slow time. Storm call. Call of Valor. Slow time. Fire Breath. Fire Breath. Slow Time. Repeat... All while easily dodging attacks and projectiles.
It is very powerful, but that seems to be the case with shouts. They are either next to useless with a cool down or monstrous without one. I played on novice difficulty. Playing on Master or Legendary with little in the way of defense (100 health, no armor or magic resistance) would keep the challenge up.
Roggvir's Amulet is a quest item and remains equipped through Diplomatic Immunity. The exploit is usable throughout the main quest and dragonborn. You do have to unequip the amulet during Sarthaal so a second restoration potion is needed. I didn't run any other quest lines. I destroyed the Brotherhood, exploited Paarthy, and scaled the mountain above Ysgramor's Tomb to obtain shouts. I'm missing only the word from Snow Veil Sanctum (3rd Disarm) and all from Dawngaurd.