The whole book seems a great Crowning Moment Of Awesome for Vetinari. We see how much he has changed the city, how positive those changes have been despite some questionable choices along the way (like empowering guilds instead of Watch), and probably the reason for these choices. And, most importantly we see that he does indeed have a heart (so doubles as a Crowning Moment of Heartwarming). Foreshadowed right in the beginning of the story where he wore lilac in the original timeline as well.
“I joined the fight. I snatched up a lilac bloom from a fallen man and, I have to say, held it in my mouth. I'd like to think I made some difference; I certainly killed four men, although I take no particular pride in that. They were thugs, bullies. No real skill.
Vimes takes down a large portion of the City Guard forces with little more than some willpower, a handful of ginger, and the greatest Ass Shove in the history of literature.
The end of the book deserves special mention when Vimes arrests Carcer (which is made awesome primarily because he manages not to murder him).
Vimes confronts the resistance at their barricade.
"I repeat, I order you to dismantle this barricade." [Vimes] took a deep breath and went on. "And rebuild it on the other side of the corner with Cable Street! And put up another one at the top of Sheer Street! Properly built! Good grief, you don't just pile stuff up, for god's sake! A barricade is something you construct!"
When the old, corrupt watch arrests him, Vimes almost escapes by threatening the guy in charge with his own sword, which is even more awesome because he works this into a rant about all the holes in their form.
This is made doubly awesome because he is then finally arrested by a younger version of himself. Whichever way you look, Vimes comes out on top.
The greatest Crowning Moment Of Awesome in Night Watch, nay for Vimes, nay for the entire series, takes place entirely in Vimes' own head:
He wanted to go home. He wanted it so much that he trembled at the thought. But if the price of that was selling good men to the night, if the price was filling those graves, if the price was not fighting with every trick he knew... Then it was too high. History finds a way? Well, it would have to come up with something good, because it was up against Sam Vimes now.
At the end, after arresting Carcer, Vetinari suggests a statue for the men who died, with a plaque to the effect of 'they did the job they had to do'.
Vimes: How dare you? How dare you! At this time! In this place! They did the job they didn't have to do, and they died doing it, and you can't give them anything. Do you understand?
That was even more awesome for Vetinari, because earlier in the scene Sam himself had mentioned a statue or something for the heroes, and Vetinari turned it around on him with deliberate use of the "job they had to do" phrase to make the insufficiency of a monument clear.
Not to mention Vimes yells at Vetinari AND GETS AWAY SCOT FREE. Though thats partially a CMOA for Vetinari as well, as he realizes at this time in this place, he can afford to allow it. But he points out to Vimes that's the only time he will.
Vimes leads a rather bedraggled group of Watchmen into battle against a much better-armed group of Unmentionables twice their size and completely and utterly owning them. A very decent proportion of the enemy ended up just running away from "a maniac with two swords." Let's just recap real quick. The evil, dark force that is the Unmentionables was half-obliterated and then chased out of action by Sam Vimes, armed with nothing but two swords and blind in one eye.
Ned's reply to Vimes finally owning up to being a time traveller. 'I traveled here through time.' Ned looks him over—post-battle—and has to ask 'From how far back?'.
One we never get to see, though it gets described: Vetinari failed his stealth final in assassin school, because his instructor marked him as absent. Let that sink in for a moment.
His Aunt also notes his repeated reprimands for not showing up for his concealment classes in general...
Vetinari's "assassination" of Lord Winder. He actually walks into a party that Lord Winder is in, takes out two miniature crossbows, shoots the bodyguards with them, then pulls out a sword. Before he can actually use it on him though, Lord Winder dies of fright. This is being done in a crowded room full of people, and Vetinari just walks out — with no one saying a word.
This becomes a neat bit of Fridge Brilliance when you notice that every previous scene had Vetinari talking about camouflage or demonstrating the correct usage there-of, only to prove in this scene that the perfect camouflage is not making people not see you, but making people not want to see you.
Which means it's even more of a MoA for Vetinari's aunt, who'd deftly arranged the crowd to ensure its convenient blindness.
Let's rephrase: Vetinari walked into a crowded room in the middle of the palace, kills the most important man in the city (and his two bodyguards), and walks back out, all without being seen or leaving a mark on his target. Assassin legends rarely do as well.
Nobody in a crowded room of nobles saw Vetinari... except his target. There's stealth, there's style, and there's Vetinari.
Really, any time Vetinari opens his mouth counts. There's a reason why one of Sgt. Colon's greatest fears is that Vetinari will get sardonic on him. Also, when he holds flowers in his teeth. Don't ask.
Reg Shoe. Though throughout the book he was a silly revolutionary (and in the entire series he was at best Plucky Comic Relief), when he realizes that the revolution has failed, and the ones who fought are being killed by the ones they put in power he raises the flag and leads the attack against the secret police, refusing to fall over or stop fighting even after an enormous number of arrows have hit him, before he finally dies- to return as an equally revolutionary zombie.
And he returned as a zombie because he refused to accept being dead.
And because he had to keep fighting the good fight. He gave his all for the revolution, he died for the cause, he clawed his way back from the great beyond to find that the whole thing had been a joke all along and he was the punchline. Young Vimes crawled into a bottle in despair, but Reg Shoe built a new revolution, made a new cause, and kept right on fighting.
Heartwarming In Hindsight when you realize that Reg Shoe eventually joined the Watch, fulfilling his purpose to fight for the people. And he does it under Vimes.
Okay - that "Mr. Burleigh and Mr. Stronginthearm" line was EPIC, even if nobody got it but Vimes.
So the Watch is slowly developing the various departments of a modern police service. It has detectives, forensics, surveillance, autopsies, traffic, fraud, internal investigations, all of that stuff. Now notice at the start of the book when Carcer kills Stronginthearm and hides on the University’s roof Vimes tells everyone to surround the building but not go up because he’s doing it himself… Vimes is the Watch’s one-man SWAT Team!
Not quite one-man. Detritus' actions here and in Jingo and The Fifth Elephant clearly put it at one-man, one-troll.
Vimes turning around the plot to frame him for theft. You might think the stolen item would end up in the locker of one of the men who set him up, but nope. It's in its owner's safe, because Sam Vimes is incorruptible, even thirty years in the past and under an assumed name.
At first it seems that the history has not changed. There are still seven graves and there is still lilac. But when you think about it, you realise that in fact, Sam Vimes has succeeded in defeating history. He held the barricades up till the morning and prevented bloodshed. His family, Watch, Vetinari, cemetery are all the same, but city might have a few hundred, if not thousand, people more than before the storm - people who owe their lives to Sam Vimes.
Vimes defuses a Powder Keg Crowd ... by deliberately making the watch house as unthreatening as possible, and channeling all their pent up energy into tending to one belligerent young man who works himself up into a hand injury.
Vimes making it back to the present just in time to learn that his wife was having trouble in child birth. Vimes ran naked and bloody through the city to fetch the only competent Doctor of Ankh Morpork and save his wife and child. He brought Dr Lawn, evaded a misplaced bazooka/shotgun shot, sat for the very long child birth and managed to see his son. Only then did he collapse from exhaustion and injuries.