Ciaphas Cain seems to get at least one of these per book, despite being... well, himself. The fact that he's bluffing most of the time generally only serves to polish the crown, so to speak.
In the first novel, For The Emperor, he manages to stop a riot involving Guardsmen (and women) from two different factions of an amalgamated regiment by declaring his outrage over the mess they've made and ordering a nearby trooper to go get mops
He gets a minor one in the same novel; after fighting a renegade guardsman in single combat, Amberly shows up with her informal retinue. The guardsman immediately points his hellgun at Cain, threatening to kill him if he makes a move. Cain's response? "Jurgen, kill him."
In The Caves of Ice, the local Adeptus Mechanicus and Administratum senior officials are horrified to learn that their facility is coming under martial law and attempt to bully Colonel Kasteen, the regiment's commander, into repealing the directive. When one of them makes the mistake of saying that she would "prefer the alternative," Cain dramatically drops his laspistol on the table and reveals in no uncertain terms that said alternative is execution for obstruction of the defense of the Imperium. This ends the debate fairly quickly.
Major Broklaw gets one a little bit later on, during another meeting where Ciaphas isn't present.
Colonel Kasteen called the meeting to order. Then she called it to order again. Major Broklaw fired his bolt pistol into the ceiling, and the meeting quickly came to order.
That's not even counting how Cain ends up destroying the Necron army hidden underneath the refinery. He does it by flooding the tunnels with eight million liters of refined promethium and then blowing it all up, producing an explosion so powerful that it buffets the Valhallans' troopship... which is in orbit.
The Ork gargant that's been stomping around through the whole novel also gets a moment when it fights off more than two dozen Necron monolithssinglehandedly. Keep in mind, the gargant is a gigantic, cobbled-together, barely functional walker, taking on a horde of millions-of-years old war machines built by the single most technologically advanced species to have ever existed, and it wins.
An anonymous ork infantryman deserves mention here: stabbed in the chest and left to die by Necron infantry, he proceeds to grab the nearest one, tear its leg off, and beat the thing with it. He dies shortly thereafter, of course, but it was Crazy Awesome while it lasted.
In The Traitor's Hand, a hovercar filled with psychotic, drugged-up Slaaneshi cultists crashes into the top-floor meeting between Commissar Ciaphas Cain and various ultra-high-level officers and governors. Cain wipes the floor with all of the cultists, saving the officers almost single-handedly, and then locates and defuses the bomb hidden in the hovercar. He follows this up with an act absolutely befitting his reputation as a Badass Longcoat when he casually walks over to the drink table for a spot of tea.
The Imperial fleet managed to get one later in the same book. Specifically, a lone cruiser, the flagship Indestructible (commanded by Captain Igor Yates) as well as the thousand-strong merchant fleet it was defending, facing down a Chaos Battleship, and winning, even though none of them had any firepower that could hope to penetrate the battleship's defenses without being obliterated in return. The cruiser, despite being out-gunned, out-ranged and out-classed, defiantly faces down the battleship and exchanges fire with it using its few long-range weapons. The cruiser is apparently crippled by the return volley, and reverses its engines, apparently retreating. The Chaos Battleship, thinking his enemy too badly hurt to fight back, as well as sensing that a Slaaneshi Daemonette had been summoned at the planet, and wishing to end things quickly, moves into short-range to finish the crippled cruiser off. As it looms over the damaged cruiser, the Indestructible quits playing dead and fires a barrage of torpedoes. With that one volley, it cripples the battleship, blowing off most of its primary armament. The ponderous battleship attempts to maneuver for broadside, but fails to notice that in doing so it has lumbered into the center of the merchant fleet, and even if none individually had the strength to hurt it, a thousand tends to add up. When the Indestructible took out its engines, the battleship's fate had been sealed.
Although a single chaos marine may not seem like much considering some of the things Cain has fought, the scene from The Traitor's Hand where he went mano a mano with a Khorne Berzerker was great. Cain not only survived long enough for Jurgen to blow a hole in its chest with his melta gun, but completely dominated the fight, deflecting the Berzerker's attacks with contemptuous ease and taunting it while he did so, making it simply one of the coolest victories he's ever had. To top it off, he called for a cup of tea even before the corpse was cold. To get an idea of how tough Khorne Berzerkers are in the Ciaphas Cain novels, later in the book five of them slaughter their way through literally hundreds of Slaaneshi cultists.
...until they met the Slaaneshi demon the cultists were summoning, which ripped them apart. Cain and Jurgen then kicked her butt so thoroughly that one of the Tallarn soldiers who witness the battle returns home to found a fringe sect of the Imperial Cult that venerates Cain as a prophet of the Emperor. To quote The Book of Cain, Chapter IV, Verse XXI:
'Then the prophet spake: saying "Frak this, for my faith is a shield proof against your blandishments."'
The real quote was pretty badass too:
"Frak this! My soul's my own and I'm keeping it!"
Cain is consistently described in his novels as one of the best (if not THE best) swordsmen in the whole Galaxy. Which speaks volumes, given that it's 40K, and Cain is basically just a normal man, if large and powerful. And it's not Cain who's saying this about him, either; it's Inquisitor Vail, whose job has likely given her the chance to see plenty of other badasses for comparison.
When he is faced with a Daemonhost in the short story The Beguiling we get this line:
"Cain to command. Full barrage, danger close, immediate effect. Don't argue, just do it!"
Which means he ordered his (artillery) regiment to start shelling his exact position with everything they had. Before trying to escape.
In Death or Glory, Cain and his band of refugees are trapped in a valley with a massive hydroelectric dam behind them and an approaching Ork warband ahead of them. Cain's solution to this problem is to blow the dam behind them as they fall back and drown the Orks. This may not sound like much of a feat, but consider that the dam had to be blown open with multiple shots from Basilisk artillery and that the warband was a fairly sizeable chunk of the invader's forces (casualties among the orks from this action were estimated at over 7000, while Cain's force was only around 300, including civilians).
Arguably, the entire plot of the novel, in which Cain goes from a survivor of an orbital battle stranded behind Ork lines to the leader of a large force of Imperial irregulars that manages to break the deadlock on the ground by striking the enemy from behind, could count as a single massive Crowning Moment of Awesome. It's no exaggeration to say that Cain's actions literally saved the entire planet in that book, especially given that his adventure culminated in him killing the gigantic ork warboss Korbul in single combat, breaking the back of the waaagh in a single blow.
The ending to Duty Calls is a piece of brilliance: After persuading a rogue inquisitor to admit him into his lair, he manages to survive contact with and apparently "purify" a Chaos Artifact of Doom that kills all who touch it. When Inquisitor Vail turns up, the rogue inquisitor discovers the ruse, pulls a gun on Cain and Vail, and flees with the artifact—only to be killed by it while making his escape, as the supposed "purification" was actually due to Jurgen's ability to null psychic power within a small radius.
Making this even more awesome is that, prior to this, Cain spends the entire meeting bluffing his way through on secondhand knowledge and bits and pieces of information he's picked up, knowing full well that the slightest slip-up in talking to these guys about things he doesn't know about will get him killed. Later on, when he's discovered, Cain uses a brilliant combination of his people-reading skills, his own massively fabricated reputation, and his opponents' paranoia to maneuver them into place to bring them both down.
"Flicker", of Amberley's retinue, gets a retroactive Crowning Moment in the same book. His backstory involves bringing down an entire criminal empire, single-handedly, against orders, with just one murder-and-frame.
Cain (unwillingly) going toe to toe with a Tyranid hive tyrant, armed with only his chainsword, and defending himself long enough to come out alive. While suffering from a minor but realistic concussion.
Praetor Kolbe's casual disposal of a Cultist interupting a vox-conversation between him and Cain.
'Excuse me a minute...' He was interrupted by a burst of incoherent screaming which sounded like the warcry of a Khornate fanatic and which terminated abruptly in a thud of a power maul on full charge and a gurgle which sounded distinctly unhealthy. 'Well he's not getting mine... Sorry commissar, where were we?'
Cain gets one when he, for once, channels the spirit of a stereotypical Commissar. A Chaos worshipper unleashes sorcery upon him that fills his mind with horrible visions of the destruction of the Imperium and the Emperor himself being devoured by daemons. Through his own will and Jurgen's psychic blank status Cain manages to throw the vision off, roars "Liar!" at the top of his lungs, and blows the psyker's head off and decapitates another with his chainsword.
In Cain's Last Stand, Cain ends the entire Chaos invasion by calling Warmaster Varan out to a surrendering ceremony... which puts Varan into range of Jurgen's blank ability, nullifying Varan's power to control his victims' minds. Cain then proceeds to take Varan on in a one-on-one duel to the death (that Cain naturally wins) which, due to Cain's skill at manipulating Varan's fragile ego, ended up being filmed and transmitted live to the entire planet. Varan's army falls apart instantly, and the entire remaining Perlian PDF finishes them offUnfortunately Varan's army just charges in a berserk fury and Cain's forces are only saved by the last minute arrival of the Necrons.
His fellow Retired Badasses deserve mention, as well. Four people, from four different departments of the Imperium (Commissariat, Navy, likely Inquisitorial forces, Adeptus Sororitas), start out clandestinely conspiring to prep their students for the coming conflict... and end up basically running Perlia's defense once the Thirteenth Black Crusade comes for a visit.
His true CMOA is posthumous. Thanks to the number of times Cain has been declared MIA or KIA and the amount of time it takes the bureaucracy to sort these out, standing orders were issued to ignore any message declaring him dead. Cain is therefore the only human in the galaxy still listed on the Active Roster despite being buried with full military honours.
Jurgen gets one in The Emperor's Finest... Cain needs Jurgen to shoot out a giant promethium fuel tank a bunch of Orks are using while staying hidden in a space hulk... Jurgen takes three shots before he gets it. Cain is disappointed that there's no visible damage to the tank... The reason? Jurgen was aiming at AND HIT the tank's release valve... at a distance where Cain didn't think it would be odd to take three shots to hit the tank as a whole.
Cain's plan is to lure the orks out and get them to fight some tyranids for him, and he's briefly worried that Jurgen's attack will end up killing them all before they have a chance to. (It doesn't.)
Cain gets several from the Reclaimers:
Being allowed to use an Astartes training chapel on the basis of his reputation as a One-Man Army. Cain compares this to having a senior priest open a sepulcher and offer him a saint's bones, and Amberly notes that he's just barely exaggerating.
Then there is the climax of The Last Ditch. Cain and Jurgen are cut off from the line of retreat, deep underground, surrounded by 'nids, and the whole area is about to become a very active volcano. So they mount up on motorcycles, and make like an action movie through tyranid made and infested tunnels.
Just the premise of The Greater Good. Cain's heroic reputation has reached the point where xenos want to ask for his help! Of course first they have to corner him and that proves pretty difficult. Cain can't see why they didn't just pick up a vox.
Also from The Greater Good, the Cogboys from the Mechanicus during the final battle. Having little else to do, they arm themselves with clubs, plasma welders, ball and chain like grappling tools, home-made bolters and grenades, one of them had a crossbow, and stuff of the like. The Tech Priest with the ball and chain catches a Tyranid gargoyle with it and saves Cain and several others from its fleshborer rounds. Cain returns the favor by cutting off the organism's tail (meant to gut the priest), guts, and slashes its wing. At this point the Priest yells, "FINISH IT!"note Somehow adding bloodlust to his/her flat, mechanical voice, proceeds to jump on it (crashing its other wing "like a ripe fruit"), and encouraging a host of Tech Adepts to jump it and hack it to pieces and pound it to paste. Cain quickly sets off to the where the Tyranids are the strongest (to keep up appearances and look heroic while actually watching out for number 1) at which point several of the lightly armed, red cloaked adepts follow him to the battle ready to get back into it. Beware the Silly Ones, indeed.