The Battle of the Last Alliance, shown in the prologue of the first film. Remember that with a few happy exceptions, fantasy movies before Fellowship were a marginalized and generally mediocre lot. With one establishing scene, Fellowship destroyed fantasy filmmaking's reputation for Special Effects Failure and Rubber Elf Ears and replaced it with the grandeur, terror and beauty that it had always striven for.
We're first shown a short clip of Sauron's orcs rampaging around Middle-Earth, before we hear Galadriel's voice say "But there were some... who resisted." Next thing we see is an army of men boldly marching straight at a massive horde of orcs at the foot of Mount Doom. We then cut to a shot of the aforementioned massive horde of orcs charging at the almost equally large Last Alliance army, who then proceed to wipe the floor with the orcs.
From the same battle scene, Elrond giving his archers the order to fire, and a volley of arrows goes flying through Elrond's line, narrowly and accurately missing their own troops to lay into the onrushing horde. Elrond himself doesn't even flinch when an arrow clips right past his ear.
As the Orcs reach Elrond's front line, the Elves elegantly carve them up in a movement that begins from the far end and sweeps like a wave along the line.
The Last Alliance just walked into Mordor. Admittedly, they did have to get rid of a few obstacles first.
And also Sauron himself demonstrating the power of the One Ring and obliterating the forces of the Last Alliance by himself, delivering a One-Hit Kill to anyone who is unfortunate to be within his reach.
As well as plenty who aren't; his mace sends some soldiers flying without ever touching them. The Dark Lord isn't just using blunt force to level his enemies.
Isildur, having seen his father killed by Sauron, picks up his father's sword, only for Sauron to shatter the blade underfoot. Does Isildur just give and die? No. Being the Determinator he is, he chops off Sauron's hand with the tiny part of blade left, separating from him his One Ring and the majority of his power, dissipating his physical body. Just One Man single-handedly took out the ultimate Big Bad of Middle Earth.
A small moment: a very large deal is made out of Bilbo being one of the few to hold the Ring and give it up willingly, and Aragorn being able to refuse Frodo's offering the Ring, but Frodo manages to openly attempt to give it up four times. Small victories that show the resilience Frodo will have later on:
The second he hears of its true nature, he is prepared to lock the ring away to keep anyone from learning about it and urges Gandalf to take it from him once Gandalf explains that locking it away isn't an option.
Explaining "the Ring will be safe in Rivendell" already willing to leave it behind.
Managing to pull it out of his pocket at the Council meeting and, aside from the pang when Gimli attacks it, otherwise has zero immediate desire to take it back until the bickering. Even then, duty takes precedence over desire for now.
At the Council of Rivendell, Gimli doesn't waste time after hearing the Ring must be destroyed. As soon as the words leave Elrond's mouth, he says, "What are we waiting for?", takes up his axe and slams into the One Ring. (Granted, the axe shatters but still). He is, in fact, the only character in the franchise to directly attempt to destroy the ring. Even Frodo succumbed to it at Mt. Doom.
Gandalf's escape from Isengard; enduring a beating from Saruman telling him he cannot resist the allied power of Saruman and Sauron, he undercuts the White Wizard's delusions as he tells him "There is only one lord of the Ring, and he does not share power!" before jumping from the tower to a passing eagle.
Another Gimli moment comes a few scenes later, as the Fellowship flees to the Bridge of Khazad-dûm. The chamber opens up and suddenly they are surrounded by thousands of orcs. The rest of the Fellowship looks terrified, but Gimli? He just hefts his axe and growls.
Also in Balin's Tomb, Frodo has just received what everyone -including him- thinks is a fatal wound from the Cave Troll. Merry and Pippin's response after their initial shock? Reverse grip their short swords, let out angry cries, jump on the Cave Troll's shoulders, and start stabbing it with a flurry of blows.
While some of the hobbits have shown bravery and courage before, the encounter in Balin's tomb really shows that they are conniving, brave, and downright dangerous if pushed far enough. Sam loses track of his sword about halfway through the fight and starts fighting with his frying pan to equal effect by smashing the orcs off walls and pillars, Merry proves a competent swordsman who shows skill on par with Boromir with the highest hobbit body-count, and Pippin is a berserker who keeps stabbing the cave troll until the last moments then has a well-timed stab that allows for Legolas to have the clear shot that finally takes it down.
The cinematic and musical richness of the Fellowship's encounter with the Argonath, the rock-hewn statues of two notable kings of the ancient border of Gondor. It draws pause to think of how really, really ancient the history of Middle-Earth is—so much that that characters really are dwarfed (sorry) by their role in it.
The establishing shot of Barad-dûr. The camera swings as it rises around the gargantuan structure festooned with buttresses, causeways and sheer black stone before the blazing summit of the Eye and distant Mount Doom fill the screen.
This then cuts to the Nazgûl pouring out of the vast black gate of the green hideousness that is Minas Morgul.
The beginning of the big fight at Amon Hen: Aragorn tells Frodo to go alone after proving that he isn't so easily tempted by the Ring (unlike Boromir mere moments prior), then he stands and turns to meet a mob of Uruk-hai, saluting with his sword in an utterly badass Slow Walk.
Aragorn's climactic fight against Lurtz lasts all of one minute, but it's hands down the most intense duel in the entire trilogy.
Aragorn, having been knocked half-senseless, swinging his sword at the last moment to knock out of the air the dagger being thrown at him. A classic action moment, elevated when you learn much of the sequence was not choreographed nor a special effect. The prosthetics that Lurtz had on — specifically the contacts — hindered his depth perception, making the headbutt that he delivered to Mortensen quite real and quite painful, nearly knocking him out cold. The punch to his gut was also not pulled, and the sound you hear him making is him grunting in actual pain. Finally, when he threw the knife, what should've been a far miss throw ended up flying straight at Viggo Mortensen's face. Mortensen deflected the knife himself. This was after the stuntman had failed several times to hit the knife out of the air.
Lurtz is absolutely no slouch at combat. He pins Aragorn to a tree by the neck by throwing his shield at him, and would've decapitated Aragorn if not for the latter slipping down the shield at the last second. A dagger stab in the thigh? Why, punch Aragorn away, headbutt him, pull off the dagger and then throw it back at him! Even after Aragorn cuts his sword arm and stabs him in the gut, Lurtz pulls the sword in deeperand tries to attack him from there, snarling at Aragorn as he does so.
That fight was so awesome, audiences all around the world have been reported applauding the cinema screens after Aragorn takes Lurtz's head off.
Boromir's crowning moment coincided with his redemption, when he charges in to protect Merry and Pippin from the Uruk-hai. Then Lurtz puts an arrow in his chest. Boromir falls to his knees, looks at Merry and Pippin, then he gets back on his feet and starts fighting again. Twice. Also bear in mind, those arrows? They were the size of tree branches.
Plus, from how well he was doing (even without his shield) until Lurtz brought in a ranged weapon, it's entirely possible that had he not left it behind, he would have won, or at least killed enough of the Uruk-hai that Merry and Pippin could have gotten away. Wide shots during his death scene reveal piles of Uruk bodies strewn all over the place. When Lurtz stands in front of him to administer the Coup de Grâce at point-blank range, Boromir stares him down, clearly in agony and exhausted, but not scared, of him or of dying. Lurtz may have mortally wounded Boromir, but he couldn't scare him.
His last line to Aragorn: "My brother. My captain. My king."
Boromir's second-to-last act before his death? Begging Aragorn for forgiveness for trying to take the ring from Frodo. His last act? He uses his own death as a Dare to Be Badass moment to make Aragorn swear to help his people and his city, by claiming that the world of Men would fall while silently begging Aragorn to tell him that he's wrong. Small wonder that this is Sean Bean's favourite of his (numerous)on-screen deaths.
Merry and Pippin deserve some credit as well. First, they bravely lead the orcs away from Sam and Frodo. Then they do their best to help Boromir by tackling and stabbing an orc twice their size and then throwing rocks at several orcs who are trying to flank him.
Aragorn's Big Damn Heroes moment on Weathertop. Frodo's just been stabbed, the other three Hobbits are clearly no match for even one of the five Ringwraiths that are surrounding them, and then Aragorn comes flying in from offscreen Dual Wielding his sword and a torch and not only holds off the five of them alone, he sends them running, culminating with one jumping off the side of the mountain to get away with him. And when the last one moves to go after the Hobbits rather than fight Aragorn when he's not looking, Aragorn turns, glares at it, and the thing pauses and looks over with body language that clearly states "I have made a serious mistake tonight" before Aragorn throws his torchinto its face and sends it jumping off the mountain.
Witch-King: Give up the Halfling, she-elf! Arwen:[draws sword] If you want him, come and claim him!
Made even better by the Nazgul's response: Instead of being intimidated, they immediately draw their swords in unison and start to cross, fully intending to take Frodo if Arwen won't give him to them willingly.
Sam's first Moment of Awesome in all the movies is the sequence after Aragorn has dragged Frodo up the stairs. While his friend is busy getting creeped out by the strange man, he pulls a drunken Merry and Pippin out of the crowd, spots Frodo being pulled away, grabs a chair and a candelabra and prepares to take down a guy with a sword. A preview to the later awesomeness with Shelob, but a Moment of Awesome nonetheless considering all we'd seen of him at this point was a complaining, not-as-bright-as-Frodo-but-not-stupid sidekick.
Just to clarify, Pippin and Merry are the ones holding the chair and the candelabra, respectively, and they both look terrified. Sam charges in unafraid ready to take on a shifty swordsman taller than all of them with nothing but his bare fists!
Sam: Let'im go! Or I'll have you, Long-Shanks!
Sam's next moment comes when the four hobbits are surrounded by the Ringwraiths. As the hobbits huddle together fearfully, Sam shouts "Back, you devils!" and attacks the nearest wraith. After doing nothing but running from them up to this point, Sam is the first hobbit to fight back.
When the Watcher in the Water grabs Frodo, Sam wades in and begins chopping its tentacles before the more battle-hardened members of the Fellowship even get back out of the mines.
He gets another one during the Fellowship's fight in the mines, singlehandedly taking out two orcs, with a Frying Pan.
Sam: I think I'm getting the hang of this. [Knocks out another one]
The entire Bridge of Khazad-dûm scene is masterfully translated to screen. Everyone runs over the bridge while badass music plays, and then tiny, frail-looking Gandalf battles a gigantic, flaming demon three times his size. And to crown it all is when he yells his famous, "You Shall Not Pass!" line. The delivery is a crowning moment of awesome in and of itself, but it shows that Gandalf is not just a charming old man who can magically shoot fireworks, but is now a supreme force of good who will face evil incarnate and kick its ass.
The Balrog itself is something that deserved a CGI animation award. If it had been even slightly unconvincing, Gandalf's big scene would have been Narm. Thankfully, it was every bit the primeval demon it needed to be. The Balrog's CGI it's so good that it still looks convincing two decades later.
Oh yes this cannot be understated! The Balrog, one of the most terrifying elements of the entire book trilogy, could have gone so wrong (see for example its almost farcical representation in the Bakshi movie) but the final result was so awe-inspiring that if Tolkien had been alive to see it he would have wept with joy!
The Balrog summons a massive sword that alone is twice Gandalf's size... and then Gandalf's bright light creates a shield around him that breaks the sword on contact. While we only get to see bits and pieces of Gandalf's magic due to Ishtari trying not to meddle too heavily in the affairs of the world, breaking a weapon of dark fire made by one of the most horrifying demons in the Tolkien legendarium is a good sign of what the Wizards' power would be if they didn't hold back.
Trapped with Frodo on the wrong side of a gap too wide to leap, Aragorn first shoves Frodo to safety when part of the pillar crumbles, nearly falling off himself, and then surfs a crumbling stone pillar, shifting his weight so that it'll topple and crash into the next part of the stairs. All this while the score builds to a tense, expectant crescendo... and then, when Aragorn succeeds, the Fellowship's theme blares forth triumphantly.
Gandalf reminding Bilbo that he's not "some conjuror of cheap tricks":
Gandalf:I am not trying to rob you! ... I am trying to help you. All your long life, we've been friends. Trust me now, as you once did.
Not as action-oriented, but: Bilbo managing to drop the Ring on the floor of Bag End and leave it behind, an incredible show of willpower on his part that's never matched by anyone else in the entire series. Everyone else who gave up the Ring had only been in contact with it very briefly - Bilbo had owned it for decades, and yet still managed to give it up.
In fact, at this point in the story, he is the only person who has managed to achieve this feat, until Sam gives the ring back to Frodo in Mordor, and even then Sam only bore it for a few days.
A quiet one, but: Frodo and Aragorn's last meeting on Amon Hen. We've just seen Boromir driven mad by desire of the Ring, attacking Frodo to get it, and reduced to sobbing and clawing at the dirt. Right on the heels of this, Frodo comes face to face with Aragorn, cringes away in fear, and then, when Aragorn realizes why, actually offers him the Ring open-palmed. Aragorn walks toward him, eyes burning in his face, reaches toward it... then drops to his knees and gently closes Frodo's hand over the Ring. This moment - the only Man able to refuse the One Ring - was given to Faramir in the book, but it is more emotional (if more predictable) given to Aragorn. Jackson observed that they never got to say farewell in the book, and putting this scene in the movie tied the resulting 'Frodo arc' and 'Aragorn arc' together.
Aragorn: I would have gone with you to the end — into the very fires of Mordor. Frodo: I know.
The many feats Legolas pulled during the Moria battle. After barring the door, the orcs try to bust their way in but the moment they made a crack, Legolas shoots an arrow through that small target to already get a kill. Later, he tricked the cave troll to wrap its chain on a pillar which Legolas climbed to reach the troll's back and shoot its head. Then at the end of the fight, Legolas shot an arrow up the troll's mouth, killing it.
In the extended version, the scene where Boromir paws the shards of Narsil (accidentally cutting himself) is a masterful job of characterization without exposition, in a scene that is nominally not even about Boromir. In just a few seconds we see Boromir's character laid bare: not malevolent or malicious, good-aligned, but foolish - impulsive, lacking due respect for great artifacts, possessed of just enough knowledge to be dangerous to himself. Contrasted with Aragorn's respectful reserve. Boromir is that tourist in Yellowstone who tries to take a selfie with the bison.
, is a crowning moment for cinematography.