Ganta's fight with Senji in chapter 8. After losing most of his blood trying to hit Crow, it looks like he's finished. Somehow, he manages to get up and gather enough blood to shoot the speaker above Crow's head. Crow slices the speaker, but this move bought enough time for Ganta to get close enough to him to shoot him point-blank in the chest.
Chapter 15-Nagi versus Hibana. Nagi's arm is smashed, and nearly severed. So what does he do? He tears it off and throws it at her as a distraction, before completing his objective of activating the elevator, and then using blood from his severed arm to activate his Branch of Sin. Rokuro admits the chances of that happening were 2%.
Chapter 21. Absolutely done with Genkaku's Ax-Crazy nihilism as he tries to gun down everyone in the room in the name of "salvation", Ganta fires the Ganbare Gun for the first time. The latter tries to move out of the way, only for Nagi (who was mortally wounded via a hole through the torso by Genkaku) to hold him down long enough to be hit. Bonus points for the Bond One-Liner he dropped before impact:
Crow can be seen as a walking moment of awesome from his behavior to Big Damn Heroes moments, especially coming up with a way to counter the Worm Eater weaponry just after he encounters it in Episode 10. "Invisible Black" is quite a fitting name for the move used too.
La Résistance and retroactively, Toto standing up to Hagire Rinichirou's insanity in chapter 52, essentially saying 'You need to get over yourself.'
Although it's one of the saddestfinalbattles, you can't deny that the battle in Chapter 56 between Ganta and Shiro is nothing short of intense to read. Watching these two put their skills to the limit makes for some pretty sweet and fast-paced eye-candy. It's an amazingly drawn and choreographed fight by any means.
Ganta actually gets in a fist-fight with the Wretched Egg and holds his own. The Wretched Egg who is superpowerful and telekinetic. It's just so audacious that he even tries it, and even more awesome that he manages to land blows without taking any good hits. The Wretched Egg even opted to back off instead of take it, and Ganta yanks him back by his leg. If that's not badass, I don't even know what is.