This exchange between Agent Simmons and Captain Lennox:
Simmons: "I'm gonna to count to five." Lennox: *shoves gun against Agent's chest* "I'm gonna to count to three."
Captain Lennox is pretty cool throughout the movie, but his CMoA is definitely during the final battle, where he charges Blackout on a motorcycle at high speed, jumps off the motorcycle and slides under Blackout to deliver a point-blank shot with a grenade launcher.
The fact that Shia LaBeouf as Sam improvised most of his rant about how the Autobots were messing up the backyard, and Peter Cullen, recording his lines in some studio miles away, goes 'Calm down, calm down' in perfect comedic timing.
Probably the moment when you realize just how insane the fights were going to be was the first robot confrontation between Bumblebee and Barracade. Bumblebee stands protecting Sam and Mikaela and Barricade leaps forward like a predatory animal and kicks Bumblebee in the face, sending him flying into the distance. Bumblebee looks up, shakes it off and rolls back to his feet and returns the favor in one swift motion.
Made even better when Sam and Mikaela are driving away in the unhurt Bumblebee— and Barricade is lying on his back as mostly twisted wreckage. Bumblebee is a FEROCIOUS animal when Sam is in danger.
Ironhide using his cannons to propel himself in the air and somersaulting in mid-air. And that was before dodging missiles from Brawl, while transforming.
Another one goes to Ratchet who uses a buzzsaw. to cut off one of Brawl's arms.
How about when the Sector Seven agents are taking the kids away, and suddenly their car is lifted several feet into the air by a 30 foot pissed off robot? While the agents can just stare up at Optimus, Prime delivers a line that would make a sane man shit himself: "Taking the children was a bad move.... Autobots, relieve them of their weapons." Prime scorning these humans who had moments before been total dicks, followed by Jazz using a massive magnet to hijack all of the Agent's weapons and reducing them to being nothing more than fleshy slag, is quite endearing.
Sam Witwicky: I'd like to introduce my friend, Optimus Prime.
The F-22 attack on Megatron stands as one for the US military. He had been in an even fight with Optimus Prime, but a single salvo of human missiles brought him to his knees.
Starscream taking on several F-22s, seamlessly shifting between his jet and robot form, and destroying about half of them before hiding among them and seemingly taking part in the attack on Megatron.
The U.S. military gets one early in the movie with their coordinated ground forces, A-10, and AC-130, forcing Scorponok to actually retreat, leaving a piece of itself behind.
The villagers get one too. They could have been hostile to the U.S Special Forces team, and they wouldn't have been unjustified in feeling that they brought Scorponok to them. Instead, they start grabbing bolt action rifles and revolvers and fight alongside Lennox and his team despite their own comparatively pitiful firepower.
Dreamwave Transformers comics
In a Transformers vs. G.I. Joe comic set in World War II, Grimlock and Roadblock are hanging onto a cliff, and Grimlock is starting to slip. He tries to get Roadblock to save himself, that he'd try to hold on long enough for him to get up, but Roadblock refuses:
"Did you say TRY? We don't try around here, soldier — do you hear me? We don't try, and we don't quit! NOW REACH!GRAB THAT DIRT! You are a lean, mean, climbing machine, and you are going nowhere but up! Sound off! I want to hear you say it — 'Me, Grimlock, going up!'"
In the second Generation 1 mini-series, Ultra Magnus takes down Menasor while still in truck mode. He does this by hurling insults to each of the Stunticons that make the Combiner. This drives Menasor insane and allows Ultra Magnus to catch air and ram Menasor IN THE FACE.
IDW Transformers comics
In Spotlight: Metroplex, Sixshot hunts the Throttlebots through (unbeknownst to him) Metroplex's alleyways. Just as he's about to kill off one of the Throttlebots for good, Metroplex pops his arm out and pounds Sixshot full-force into the ground with his fist. And then Sixshot stands up again. So Metroplex transforms into his ridiculously gigantic robot mode and steps on Sixshot. (In a splash panel spanning two entire pages, no less.) At the end of the issue we see that Sixshot is still alive and moving after all that, albeit quite crushed and mangled. Really it's a case of both the good and bad guy getting a moment of awesome at the same time.
In the Steampunk story Hearts of Steel, Mark Twain manages to singlehandedly defeat Ravage with a lit cigar and a gas-filled house.