The nameless dryad who, despite being in agony due to the fact her tree was being cut down, nonetheless travelled for miles on foot in order to take news of the destruction to King Tirian and warn him of the Calormene's treachery.
Peter rebukes Tash and sends him packing with what is probably the Narnian version of "The power of Christ compels you!".
Then Tash turned his head sidewise to fix Tirian with one of his terrible eyes [...] But immediately, from behind Tash, strong and calm as the summer sea, a voice said:
"Begone, Monster, and take your lawful prey to your own place: in the name of Aslan and Aslan's great Father the Emperor-over-the-Sea."
The hideous creature vanished, with the Tarkaan still under its arm.
Tirian in the Last Battle, particularly throwing Shift into the stable.
There's also Jill. Her last adventure in Narnia had some scary parts, but everyone ended up getting through alright. Here, she, Eustace, and Tirian basically enter a hopeless battle and watch countless allies being mercilessly killed in front of her. She understandably is very upset and begins to cry, but still keeps the presence of mind to turn her head away so she won't ruin her bow with her tears and be unable to keep fighting.
Emeth the saved Calormene, who worshipped Tash so sincerely that he walked into what he thought was the presence of Tash even though he expected to die on the spot, and then Aslan gently tells him "Child, all the service thou hast done to Tash, I account as service done to me." This also counts as a Crowning Moment of Awesomeand a Crowning Moment of Heartwarming for C. S. Lewis the theologist. The meaning of Aslan's speech is that it does not matter what name you call God, as long as you follow out of a sincere search for truth rather than just paying lip service to religion.
A troper on the Awesome page for The Silver Chair says a speech from that book is a good summary of why they still have religious faith — this part from TLB is the cornerstone of what this troper believes (no matter what anyone tries to say), and I first saw it here when I was too young to know what I was seeing.
And still more awesome is Emeth's own honesty when he sees Aslan and thinks "Oh, Crap!, I should have been worshipping him all along, and he must know I haven't" - and he admits the shameful fact to Aslan himself.
And as a nice bit of trivia, the word 'emet' is Hebrew for 'truth'.
The return of Reepicheep.
Seeing virtually every major named, Narnia-born supporting character return is probably a general Moment in itself, as well.
Jill sneaking Puzzle out of the stable.
For the sheer OHCRAP!!! factor, the scene where Rishda comes face-to-face with Tash:
Tash: "Thou hast called me into Narnia, Rishda Tarkaan. Here I am. What hast thou to say?"