Tyreese's Last Stand in Issue 14: After witnessing the death of his daughter in a failed suicide pact, he opts to aid the group in taking out a group of zombies in the gym. When entering the gym, he runs straight into the middle of the zombies, killing as many as he can before the group are forced to leave. In the next issue, they return to find all of the zombies dead and Tyreese alive in the corner of the room, casually greeting them.
Rick is holding off the zombies alone so that Dr. Cloyd can treat Carl's gunshot wound. He's being overwhelmed. Cut to each of the members of the group seeing him fighting alone, and each one of them going out to help fight them. In a series devoid of optimism, this doubles as a Crowning Moment of Heartwarming.
Volume 16: A Larger World
Jesus in his introduction takes on Michonne and Abraham barehanded, while they are armed with their classic katana and rifle. Jesus manages to disarm both, then capture Michonne to use as a human shield.
Volume 18: What Comes After
You thought Carl killing three zombies by himself was awesome. Wait until you see the moment when he hops out of the back of one of Negan's trucks and blows away about half a dozen of his men with a freaking assault rifle. And that assault rifle belonged to the late Abraham's, to boot! This moment impressed Negan so much, that he decides to invite Carl into base as a guest just as much as a prisoner.
Volume 21: All Out War (Part Two)
Issues 125 and 126, which conclude the All Out War arc, depicting the climactic show down between Rick, his allies, and Negan's forces. After Negan demands surrender, Rick comes out from the Hilltop to parlay and hits Negan with a positively devastating "The Reason You Suck" Speech wherein he calls Negan out for being a world-class hypocrite and essentially says to him "Hey, maybe if you'd stop being such a murderous prick and actually live up to your rhetoric about rebuilding civilization, maybe we could actually work together and do that instead of killing each other like idiots." But even better? Against all odds and expectations, Negan actually realizes that Rick is right and starts seeing things his way. Then, as soon as his guard is down, Rick slashes him in the neck and triggers the ambush that (in part) ends the war in his favor.
But that's not even the best part. After finally defeating Negan and ending his reign of terror, Rick refuses to let his hated enemy die and actually insists that they save his life. Why? So that they can deliver him to legitimate justice, prove that the new society he's building can be humane to its enemies, and so that Negan will be forced to watch the new world he envisioned thrive without him. After enduring two years of constant tragedy and brutal loss, after watching himself slowly lose his humanity and become little more than a savage, ruthless animal, even a murderer, Rick actually turns it all around. Rather than simply continuing to perpetuate the cycle of violence that he had previously surrendered to, Rick shows immense personal growth and vision, and triumphantly reclaims the nobility of spirit that he had long ago abandoned. Why is this arguably the most awesome of all The Walking Dead's awesome moments? Because after more than 100 issues of brutal, unrelenting cynicism, the story and our hero suddenly rise from the muck to defiantly embrace idealism and optimism despite a world gone mad.
Volume 23: Whispers Into Screams
Jesus on foot armed with a sword against half a dozen Whisperers armed with knives and a flock of walkers. He kills them all, takes a Whisperer as prisoner, and saves his friend.
After the time skip, Carl is jumped by two bullies armed with a brick, who plan to kill Sophia, and mock Carl when he retreats. Carl then immediately comes back once he finds a shovel, and beats (and nearly kills) the two of them while they beg for their lives.
When the bullies' parents are reprimanding Maggie for Carl's near killing of their children, Carl rebuts them with these lines, further cementing Carl's dark side.