Frank Miller's Sin City comics are full of Moments of Awesome. Marv's best might be breaking down a barred metal door through pure stubbornness.
Or it could be at the end of the original Sin City, when Marv is sent to the electric chair. After the switch is thrown, he coughs out, "is that the best you can do, you pansies?" They have to electrocute him a second time to finish him off.
Truth in television since more than a few death row inmates have been known to survive several jolts from an electric chair. Though none were coherent enough afterward to trash-talk the executioners.
You have to hand it to Marv when he can turn simply standing up into a Crowning Moment (he doesn't hit girls).
Though he does quite calmly shoot one in the head in the Silent Night one-shot. Seems he's willing to bend the rules when it comes to child abuse.
Though Frank Miller hasn't exactly been clear on whether she's actually a woman, so it may not actually count.
Marv is given a confession to sign by the DA where he takes responsibility fro the murders of Kevin, Cardinal Roark and the girls they murdered. If he doesn't, they'll kill his mom. Marv breaks the DA's arm in three places then signs.
Or when Marv says to Roark "you can scream now if you want."
The immortal exchange between Marv and "Padre":
Padre: And what have been your sins, my son?
Marv: Well, padre, I don't wanna keep you up all night, so I'll just fill you in on the latest batch....
In The Big Fat Kill Dwight waxes poetic about the three hundred Spartans who held off the entire Persian army at the Hot Gates, a narrow mountain pass. Sure, they all died, but by carefully chosing their terrain they were able to sell their lives dearly. Later, Dwight and the girls of Old Town are massively outnumbered by the gangs, so they lure them into a narrow, crooked alley, where Dwight reflects that "the choice of where to fight can mean a lot but there's nothing like having all your friends show up, with LOTS of guns.
In That Yellow Bastard Hartigan has his first at the end of the first issue ("I take his weapons away from him. Both of them." goes the captions while he shoots Junior's hand holding the gun and then his crotch) but probably his greatest at the very end: "An old man dies. A young woman lives. Fair trade."
'The kids a decent shot, but he's throwing bullets away like they're candy. He doesn't know how to aim true, look the devil in the eye.' * BANG*
Pretty much every time Miho appears she gets at least one crowning moment of awesome.
Such as taking Jackie-boy's hand and wiping out everyone in the car.
Hartigan breaks a window and grabs a piece of glass with his feet to cut his bonds. While hanging from a noose.
Dwight orchestrating the utter ruin of an entire mob family in the span of a single night in Family Values.
Marv kicking the crap out of an entire squad of government agents, finally turning to the leader and saying "That there is one damn fine coat you're wearing."
Wallace letting Manute know what body parts will be broken if he attacks him... and then apparently keeping his promise.
Dwight has just been shot up. He's bleeding to death, he's now wanted for murder, and the police are on their trail. Marv drives him to safety, running cop motorcycles off the road and dodging oncoming traffic... all while discussing modern country music.
Marv vs. Manute.
Marv revealing that he broke through his restraints and had been willingly taking a beating from the Old Town girls just to prove his innocence.
In Family Values, we get a scene with about three CMOA in the span of a few pages. Miho is casually taking down a mob enforcer, chopping him up before kicking his head clean off (for throwing around Japanese slurs). Dwight lets two other mob enforcers watch. They happened to be brothers. Dwight tells one of the brothers to kill the other. When he refuses, Miho takes a moment out from toying with her prey to throw a shuriken, slicing his cigarette in half from across the parking lot. He obliges and shoots his own brother out of fear.
Later in that same story, Miho is apparently asleep in the backseat of a car. The same mob enforcer decides to sneak his gun out of his jacket. She quickly opens her eyes and unseaths her katanna by just an inch. The enforcer puts his gun away and she calmly goes back to sleep.
"Deadly little Miho. You won't feel a thing unless she wants you to." (Happens quite a few times, so take your pick.)
Wallace shooting a sniper through his own scope.
Wallace taking down an entire factory filled with assassins before any of them can really react. The fastest one "almost fires a shot."
Marv versus Kevin, the entire fight.
Nancy Callahan killing Senator Roark and avenging Hartigan.
Johnny's Establishing Character Moment sequence has him showing off both his knack for good luck (by beating the slot machines in a manner that would please Fonzie) and his immense sense of style (his coin flipping).