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.
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 Epic Mount. 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 helicoptors around like ragdolls. And it works. The look on the Na'vis' faces when he flies in on it is priceless.
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.
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. 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.
Neytiri killing Quaritch with two arrows straight through the chest.
Jake landing on 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 round.
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.
What's notable about the all-time domestic tally of the film is that it didn't even have a triple-digit opening weekend. It opened with a $75 million take, which was the highest opening for an original (non-sequel or adaptation) film ever, but still well below heavy-hitting franchise films. The result is that while it didn't come close to an opening weekend recordnote for perspective, The Avengers opened with nearly triple that of Avatar, it demolished the 2nd-weekend recordnote now held by The Avengers as well by posting a near-identical grossnote where most blockbuster films — and a good portion films in general — lose 50-65% of their first-weekend audience, and set X-weekend records through its 7th week before being stymied by Titanic's back-end weekend records. James Cameron doesn't just make box office history, he makes films that define Long Runner and have people seeing it for weeks or weeks, whether it's their first time or 27th.