At the final resolution of the second book Dark Adeptus, a high ranking tech priest named Saphentis won his last fight with awesome. Challenging a far more superior enemy, he was badly outmatched and quickly beaten. As his foe decided to indulge in some pre-execution taunting of the now broken and helpless Saphentis, the pragmatic tech priest taunted back to get his enemy to lower his face to his. Once close enough, he rerouted the power of his severely wounded mechanical body into his last prism eye to overload it, causing it to explode and riddle his enemy with glass fragments and giving Saphentis an opening for a last desperate charge that pinned them both in place to be crushed by a titan. Even for a half-man/half machine, it takes a special level of pragmatism to use your own eye for a directed explosion out of your very skull. Skull did not fare well, by the way.
Another one from the Warhammer 40K line, this time from the Grey Knights novel. Justicar Alaric and a small team of his Grey Knights were about to face one of the most terrible daemons in the galaxy. In fact, it was one so terrible that it once massacred over 300 Grey Knights in one battle. To inspire his men, he gave this awesome speech:
"We do not know what our chances of survival are, so we fight as if they were zero. We do not know what we are facing, so we fight as if it was the dark gods themselves. No one will remember us now and we may never be buried beneath Titan, so we will build our own memorial here. The Chapter might lose us and the Imperium might never know we existed, but the Enemy - the Enemy will know. The Enemy will remember. We will hurt it so badly that it will never forget us until the stars burn out and the Emperor vanquishes it at the end of time. When Chaos is dying, its last thought will be of us. That is our memorial -carved into the heart of Chaos. We cannot lose, Grey Knights. We have already won."
The Sisters of Battle, arguably, have a CMoA in this book:
Alaric: "I'm just glad they're on OUR side."
Ghargatuloth himself has an epic moment despite being the villain of the first book, when he is revived and the extent of his scheme becomes clear. He manipulated events behind the scenes for thousands of years, including purposefully setting up an Imperial Saint and gradually corrupting the Trail of Saint Evisser with innumerable deep-cover Chaos cults in order to facilitate his rebirth. Then he goes on to explain how he manipulated the Grey Knights themselves, knowing that he could count on them to believe that the sword of Mandulis would banish him again when it was actually the final piece needed for his rebirth, essentially making a mockery of the entire Grey Knight order and the sacrifices they made a thousand years ago. Ghargatuloth ain't a greater daemon of T'zeench for nothing.
And Alaric survives, and in the next book, along with less than ten Grey Knights, a few Mechanicus adepts and Inquisition agents managed to take down the Castigator, the Father of the Titans (basically the original and most powerful titan ever created), the daemon who possessed its data core and fool a Chaos Lord to destroy an entire chaos titan legion.
Alaric's Crowning Moment Of Awesome from Hammer of Daemons involves him gradually losing his efforts to avoid possession due having his psychic defenses nullified, but suddenly and finally overcoming the attempt by an ageless, Tzeentchian daemon with a single sentence.
"I wish for a world where your kind cannot exist."
That moment is great, but not the real CMOA. The true Crowning Moment occurs just after that, when the daemon makes yet more attempts to possess him. Alaric is on his last legs, and with the Collar of Khorne suppressing his psyker abilities, the only thing holding back the daemon is his own willpower. Realising that the daemon is never going to give up, Alaric summons up every image of bloodshed, every atrocity he's ever witnessed, every horrifying and sanity-blasting memory he has. And then he stops resisting, driving himself insane in the process. Lets repeat that, he stopped himself from being possessed by voluntarily going mad. Wow.
Yeah, Alaric is the kind of guy who will always have a quote before stomping some daemon. And don't forget at the conclusion of the novel he starts an uprising which destroys an entire Khorne Daemon World and sabotages a Black Crusade, and he survives and return to the Imperium. All without any help from his Chapter.
Oh, yes — at the end of destroying an entire Daemon world, which you might think distracting, he finds an eldar gladiator trying to stow away. He explains that talking to him, he had indulged in Feed the Mole and knows that the eldar was a spy. No detail is too small for him in cleaning up that world.
Not only knowing that the eldar was a spy, but also not an Eldar as he claimed to be, but a Dark Eldar Mandrake
Every single book of that series contains several CMoAs. Let's take the first book, where Alaric, before going off to fight Ghargatuloth, receives a communication from Legeia that seems to be gibberish. In the battle, after Tancred falls, Ghargatuloth is ascending, and it appears before Alaric and asks him if he has any last words. He proceeds to repeat the gibberish, which he realized was the daemon's True Name, stunning and horribly injuring it.
The strike cruiser is about to go down. They're on their final deployment run. Nobody in the crew is going to survive, because they're charging straight at the planet's atmosphere so they can launch drop pods before the ship blows up. Hitting the atmosphere will be like ramming the ship into a solid wall. The following exchange occurs between Alaric and a crew member:
"Good work, officer. What's your name?"
"None of us have names. Deployment in six minutes, brother-captain. The Emperor protects."
Medic Haggard from Hammer of Daemons also deserves mention alongside Alaric. A simple man who had survived many years on a Daemon World, Haggard nonetheless managed to remain sane and helped Alaric throughout his imprisonment, saving his life several times in the process. He then joins in the revolt and manages to escape on a ship, only to find the ship had already been infested by a millenia-old Tzeench Daemon (the same one that nearly possessed Alaric, and one he had failed to completely kill). The Daemon would proceed to kill all the other survivors, but Haggard would get his revenge. He sent the ship hurtling straight into the warp, which resulted in the Daemon being obliterated by Tzeench for failing to give him thousands of souls as he had promised. Haggard's victory was so complete that while the Daemon shrieked in horror, Haggard was laughing.
The Emperor's Gift protagonist Brother Hyperion has a CMOA mid-way through the book. During the First War for Armageddon he used his psychic might to hold back Angron, who had become a vastly powerful Daemon Prince and was even bigger than the 14 Bloodthirsters that guarded him! Hyperion nearly dies doing it but he manages to break Angron's weapon, the Black Blade. Even Angron was shocked by it. It is so amazing that the Space Wolves chapter named him Hyperion Bladebreaker, and they are not easily impressed.
In the same novel, Logan Grimnar gets one when he takes down Grandmaster Jorus before he can even unsheathe his blades.
And Bjorn the Fell-Handed receives one when even Hyperion bows to him in respect.