Was just randomly thinking about how many times the dragon's been broken thus far.
So far I've got, in no particular order:
Events of the Battle of Red Mountain (Numidium, apotheosis of the Tribunal)
The Time-Wound on Snow-Throat
Activation of Numidium by Tiber Septim
Activation of Numidium in the Warp in the West
Return of Ysgramor
Pelinal Whitestrake
The Maruhkati's Dance on the Tower
Defeat of Alduin (a literal Dragon-Break)
Auriel's dracochrysalis (I'm assuming that's the dragon-break that Mannimarco mentions in "Where were you when the dragon broke")
Am I missing anything? I was wondering if other events also counted as dragon-breaks, like Martin becoming the Avatar of Akatosh, or Alinor's Mirror-Logicians continuing defense against Numidium?