The preceding scene, in which an army of mecha take a charge by a massive herd of hammerheaded titanotheres, in which the former are tossed about like ragdolls. The music for that scene is just epic.
The entire scene where Jake first meets Neytiri. Justifiable amounts of Scenery Porn and the western music make one epic scene.
Similarly enough, the scene where Jake and Neytiri visit the tree of souls. So... Pretty...
During the final battle, Colonel Quaritch's gunship takes fatal damage, and an explosion causes his shoulder to catch on fire. He runs into the cargo compartment, jumps into an AMP suit, closes the canopy, and then he puts his shoulder out. Yes, he did all of this while on fire.
Tied into this is the fact Quaritch deliberately opened a sidehatch aboard his ship and tried to shoot Jake to stop him fatally damaging his gunship, all while holding his breath (not having a gas mask on to protect him from Pandora's toxic atmosphere). It didn't work, but points for trying.
Another one for Quaritch just before the above example; with the RDA flotilla being torn apart in the air, Quaritch personally takes command of the battle; using his gunship as bait to cut a path through the rampaging ikran to get the bomber to the Tree of Souls. Were it not for Jake descending from above to take out the bomber, it would have worked.
Prior to the final battle, Jake needs a way to get the Na'vi to trust him again. Remembering a story Neytiri told him, he goes out, finds a Leonopteryx, and decides to claim it as his Cool Horse. The awesome part? This thing nearly ate him the last time they met, and he's attempting to leap onto its back based on a behavioral hypothesis he just thought up. In other words, he's Indy Ploying his way onto a creature big enough to toss helicopters around like ragdolls. And it works. The look on the Na'vis' faces when he flies in on it is priceless.
Let's expand on this. Neytiri explains that Toruks choose their riders, and that only five people in their known history have ever managed to do so. So Jake, a human in an Avatar body, did something only five other Na'vi had both the guts and strength to do, further cementing just how awesome this is.
The Sky People have sent us a message...That they can take whatever they want, and no one can stop them. Well we will send them a message. You ride out as fast as the wind can carry you... You tell the other clans to come. You tell them Toruk Makto calls to them! You fly now, with me! My brothers! Sisters! And we will show the Sky People... That they cannot take whatever they want! And that this... this is our land!
A subtle one, but the sight of Norm hustling into battle. Remember, this guy's just a normal scientist. He can keep up in a war because he has an Avatar, but it just died and kicked him back into his real body. So what does he do? He grabs a rifle and a gas mask, then rejoins the fray.
For much the same reasons, any of the Human Marines. They all volunteered to live for months or years at a time on a planet full of giant killer animals, where even the atmosphere is completely toxic.
Tsu'tsey's attack on the Valkyrie shuttle, even if it culminates in his demise. Talk about a way to go out!
When the Marine who Trudy knocked out during their rescue of Jake, Norm and Grace starts to wake up, Max punches his lights back out, quipping afterwards "That was oddly satisfying."
Towards the climax of the film, he commandeers an enormous mining machine with a spinning blade on a crane at the front of it, drives it up to the command centre, flips off Selfridge, and uses the blade to trash the command centre, sending Selfridge and everyone running for cover. While this was happening, the rest of the Avatar Project staff quickly stormed the link room and linked to their Avatars, then took the command centre and captured Selfridge and his staff.
Lost, at night, alone on Pandora, and surrounded by snarling panther-like creatures called Viperwolves, Jake has one thing to say to the beasts circling just out of reach: "I don't have all goddamn night!"
Trudy ditching the destruction of Hometree. At first it seems like she's about to pull a Face–Heel Turn as her thumb hovers over the firing mechanism. And then...
The ikran getting the marine from behind and biting his head before throwing him out of the Samson.
Having lost her ikran Seze, Neytiri claims a new mount once Eywa sends all the wildlife on the attack. Her Cool Horse of choice? Why, none other than a Thanator, the apex land predator of Pandora! Bonus point because the thanator offered her a ride!
As Jake is about to have his throat cut, Neytiri, finally able to free herself from her fallen mount, grabs her bow and, with seconds to spare, lands a truly spectacular shot that misses her chosen mate by inches and mortally wounds Quaritch. Then she puts one more massive toxic arrow in him for good measure.
Immediately thereafter, after failing to get any response out of Jake's Avatar body, it takes her seconds to figure out where Jake's real body is, what it looks like, what the mask hanging near him does, and how to put it on him. In total, the time between her killing Quaritch and saving Jake takes about one minute.
Jake landing the Toruk at the Tree of Souls, much to the clan's surprise.
The Toruk throwing helicopters into the sides of mountains.
Mo'at's first appearance - her voice has that quality where everyone can't help but stop and look her way.
She also proves that, despite her days of riding/flying being long past, she's still got nerves of steel. When the bomber approaches the Tree of Souls during the final battle, she's right there in front of it, alone - they aren't taking it without going through her first.
Before that, during the destruction of Hometree, she slowly approaches Jake while he's still tied up - she has every reason to distrust him, to kill him right there for bringing this upon The People, even has the knife at his throat... before she makes a choice that would ultimately save them all (by allowing Jake to become Toruk Makto):
Mo'at: (through tears) If you are one of us... help us... (cuts his restraints)
In the final battle, Trudy comes flying in for a Big Damn Heroes moment—raining bullets on the Dragon gunship just as it was about to shoot down Jake—and pulls dramatically around to face Quaritch. She then says in the driest, most ironic deadpan ever, "Oops."
Jake verbally serving Grace near the beginning of the movie. They wanted his brother, but got him because his brother got murdered, and since he has virtually no experience, Grace doesn't want him. She finally asks him what made him think he could come out to Pandora and work in the Avatar Program. Jake's response:
Jake: Maybe I got sick of doctors telling me what I couldn't do.
The extended opening also shows that tigers, having been extinct for over a century, have been cloned back into existence. Earth may be a Crapsack World with most of nature gone, but humanity is at least trying to repair the damage as well as it can.
