Big No/Comic Books

In the series Star Wars Knights of the Old Republic, Big Bad Haazen has one of these right before getting annihilated by the combined firepower of an entire fleet of warships.
In a flashback in the Thunderbolts 1997 Annual, Melissa Gold (in her costumed persona of Screaming Mimi, possessing sonic powers) obliterates a portion of forest, liquefies the ground around herself, and destroys her vocal chords upon the death of her boyfriend Angar, by falling to her knees and screaming for 48 minutes straight, until she shreds her vocal cords and can't do it anymore.. She gets better.
In an issue of the Sonic the Hedgehog comic (#135), this is Sonic's reaction to the apparent (and brief) death of his father, represented by him screaming helplessly with a big "N" and "O" to either side. It... doesn't really work. Points for trying, though.
In the original Transformers Generation 1 comics, Prowl got a classic one in response to the second death of Optimus Prime.
Sillage: Nävis, at the end of the first book.
Batman's reaction to the death of Jason Todd.
In Batman: Year One, Gordon's reaction to his infant child being dropped from a high bridge. Luckily, Batman saves the day.
Inverted by Black Bolt. He may only whisper "no", but the extreme volume of his voice would make the whisper loud enough to blow up a planet.
In an issue of Valiant Comics' The Legend of Zelda, Zelda points out Link's defeating Ganon is pointless because "You don't have to join Ganon! You've become Ganon!" You can guess Link's response.
In The Darkness, Jackie Estacado when he learns that he Can't Have Sex Ever.
In Final Crisis, Overman's reaction to finding out his beloved cousin Kara Kant/Overgirl is dead. Since he's German, he goes "Neinnnnnn!"
When Jane Foster is killed (don't worry, she gets better) in The Mighty Thor #371, Thor spends an entire page smashing stuff up while shouting "NO!". He ends up kneeling in the wreckage, saying one final, very small, "No."
In Uncanny X-Men #300, Fabian Cortez is informed that he's no longer the top contender among the Upstarts.

Cortez: How could I possibly lose the points for Magnus's death, unless…? (his eyes suddenly widen) NOOO!