In Necropolis, Scarlett unleashes a typhoon on Old One-occupied Hong Kong and obliterates it entirely. Terrifying? Yes. Awesome? Hell yes.
The finale in Oblivion, in which the British Royal Navy (albeit, by accident) nukes Hell.
Richard's improvised Molotov Cocktail on the monster dogs. Keep in mind that Richard was never a fighter to this point, spending most of his life in his office as a journalist. To be able to so calmly form the weapon, under such pressure, with enough precision, throwing it at the monster dogs was pretty cool.