In Attack on Titan, Mikasa decisively shows how much of a badass the other humans consider her in-universe by invoking this when the military surrounds her, Armin, and Eren right after his first Titan-shift. No one dares to advance on them with swords because she's stated to be worth one hundred regular soldiers.
Of course, this could have also been them being strapped for competent manpower, and not wanting to lose Mikasa by killing her.
Likewise, the finale of the first season of The '90sSailor Moon has each Senshi holding off a group of youma to give Usagi a chance to face the Big Bad. Their deaths were rather gruesome, and censored from the DiC English dub, which took out half the two-part episode — the remainder was merged into one.
Legend of Galactic Heroes has a suitably epic one at the Battle of Marr-Adetta when old, retired admiral Alexander Bucock and a mishmash fleet of 20,000 starships stands up against military genius and Kaiser of the Galactic Empire Reinhard von Lohengramm with 100,000 starships in multiple fleets commanded by his best admirals - and proceeds to stop Reinhard's forces in their tracks while inflicting massive casualties on them. He uses his flagship alone to shield the withdrawal of his surviving forces and when ordered to surrender, refuses and goes down smiling and drinking a toast to democracy.
Deliberately pushed to ridiculous extremes in the Excel Saga episode "Menchi's Great Adventure", where the members of Menchi's group rapidly sacrifice themselves in succession until only Menchi is left.
An example taken from the original manga. Kouji has been cornered by several Mechanical Beasts, but Sayaka shows up with Aphrodite-A to give him time to reach Mazinger-Z: 
Episode 6: A Mechanical Beast is trashing one city to keep Mazinger-Z and Aphrodite-A busy as a second Beast and a squad of Iron Masks take over the Photon Atomic Research Institute. Kouji tells he will deal with the first Beast to let Sayaka go to protect the Institute.
Another example taken from episode 74: A Mechanical Beast was completely trashing Mazinger-Z around. Sayaka -as piloting Aphrodite-A- stepped between both and stood in the way of the Beast to protect Kouji, receiving all its attacks to prevent it from killing Kouji and destroying Mazinger-Z even though it meant Aphrodite-A was destroyed for good.
Episode 92: Kouji is hurt and can not fight, so Boss knocks him out, and he and Sayaka deploy their Humongous Mecha to try to hold back the Mykene Warrior Beasts marching towards the Institute. They fail badly.
Chapter 6 from Shin Mazinger Zero: Three assassins Robot Girls -Gamia Q1, Q2 and Q3- are attempting to get Kouji murdered, but Sayaka and Boss to step in the way to protect him: 
Each member of the Sound 5 drops behind to stop or slow down the Sasuke retrieval team. The retrieval team in turn leaves a single member to fight the Sound ninja while the rest carry on; at the end only Naruto is left to chase Sasuke.
It was shown in a flashback that a team led by the Second Hokage was surrounded by an elite group of shinobi in a dangerous mission. Deciding that his charges are too young to die and they could lead the village on without him, he chose to be a decoy to let them escape and die in battle, but not before appointing Hiruzen Sarutobi as the Third Hokage.
Originally it was Louise who was supposed to delay the army by using her Void magic against them. She and Saito were well aware that this was a suicide mission, which is why Saito drugged her and took her place.
In Zatch Bell!, Won Lei does this against the massively more powerful than him Unko Tintin during the Faudo Arc.
Both exemplified and inverted in Saint Seiya. Not only are the Gold Saints tasked with barring the heroes' progress through the Sanctuary's Twelve Zodiac Houses, but whenever two or more of said heroes arrive at each House, one of them will invariably stay and fight to let the other one (usually Seiya) press onwards instead of fighting the single enemy as a team. During the Hades story arc, when the Gold Saints are allies to the heroes, they repeat their feat by holding back the spectral forces of the dead, risen to invade the Sanctuary and kill Athena. Taurus Gold Saint Aldebaran takes this to the extreme, with his body continuing to protect his House long after he has been killed.
In a parody of the above, the first Ranma ˝ movie presents the Seven Lucky Gods of Martial Arts blocking the title hero's advance in exactly the same fashion, until one of his allies (or, at one point, an entire crowd of them) arrives to take over the fight for him.
This is actually a repeat of an earlier gag in the anime, where Natsu, Take and Ume, the three elders of the Daimonji School of Martial Arts Tea Ceremony (and anime-only characters) try to bar the desperate charge of Akane, who is attempting to save Ranma from being "sacrificed", only to be knocked out of the way by the Foe-Tossing Charge of her uncontrolled horse.
C.C. pulls this in the first season finale of Code Geass, sacrificing herself to deal with the disoriented and crazedJeremiah Gottwald in the nigh-invincible Humongous Mecha, dragging said mecha and her own mecha into the ocean so Lelouch can hurry on ahead to rescue his sister. Since C.C. has already proven herself immortal (surviving a headshot in the first episode), however, the element of danger and loss is lessened.
In R2 Episode 2, Urabe of the Four Holy Swords pulls a Taking You with Me with his Knightmare's Self-Destruct Mechanism to hold off the seemingly invincible Vincent KMF. When Lelouch tries to stop him by saying that he can't build the future on the bodies of the fallen, Urabe goes ahead with it but tells Kallen to stick with Lelouch, since that the response just proves he's a man worth following. Sadly, the Vincent is completely unharmed.
In R2 Episode 10, Li Xingke says this to Zero, who had kidnapped the Tian Zi to stop the marriage between her and Odysseus.
Villain example: Cinque performs this against a berserk Subaru to allow her sisters to escape with their captive in Magical Girl Lyrical Nanoha StrikerS. She barely survives the beatdown, but she is effectively out of commission for the rest of the season.
Also, to note, indeed, "You shall not pass!" is also what she says to Subaru before her final attempt at killing her... and it also counts as practically the last thing Cinque says all season.
Haji pulls this one in the finale of Blood+, holding back a rampaging Amshel long enough for the rest of the motley band to escape. Military forces arrive seconds later and bomb the building, collapsing it and burying both of them under several tons of rubble. However, it is very heavily hinted in the final episode that Haji managed to survive.
Previous to that, Haji does his damnedest to perform a You Shall Not Pass in episode 21 against the Schiff — all of them. It doesn't quite work, but it's still pretty badass.
Tasuki attempts one of these in Fushigi Yuugi. His fight with brainwashed Tamahome is already rapidly going downhill when Nakago arrives to finish things. At this point, having already suffered a savage beating from Tamahome and barely able to stand up straight, Tasuki continues to throw himself into battle against both men, hoping to keep them preoccupied long enough for Chichiri and Miaka to get to safety. Definitely his CMoA.
In One Piece, a villain pulls this against a rampaging hero in the Impel Down arc. He even gets in a good Breaking Speech about why the hero's actions might not be for the greater good, and may in fact put the world in greater peril.
Interestingly, an inversion of this is given moments later by an extremely pissed off Magellan, who delivers a You Shall Not Leave after he finds his bruised and battered subordinate. Magellan becomes a Advancing Wall of Doom after delivering a shout so epic that it's heard several floors above him, and makes all the escaping inmates freak the hell out.
Warden Magellan:STRAW HAAAAT!! I WILL NEVER LET YOU GET OUT OF THIS PRISON!
Also pulled by Luffy in his fight against Rob Lucci, in a way, as this trope was pretty much the entire point behind their fight, as Luffy could not let him leave his sight; he was the only one capable of matching Lucci's strength, so if he let him go, it would likely spell doom for his True Companions.
In fact, both sides were pulling this trope in that fight. Lucci's reason for fighting Luffy (aside from being a Blood Knight) was to prevent Luffy from going after Spandam and Robin to rescue the latter. Lampshaded at the beginning of the fight, with Lucci's fairly casual line after Luffy tries to avoid the fight by simply rushing past and Lucci easily intercepts him and hurls him back.
Rob Lucci: "I can't let you pass." At least let me say that.
Happens again, with another villain, when Vice-Admiral John Giant (whose last name means exactly what you'd think) stands in the way of Whitebeard, and utters the exact line. It becomes a subversion when despite his colossal strength he's unable to even slow Whitebeard down.
Beautifully done by Whitebeard in a slightly later chapter. Nothing says "You Shall Not Pass!!!" quite like splitting the entire flipping island in half with a giant chasm.
When the Dressrosa arc devolves into a massive brawl throughout the country between Doflamingo's forces and the various rebel factions and gladiators seeking his head, the only thing keeping the Marine force led by Admiral Fujitora and including at least two Vice-Admirals from helping Doflamingo's side is one lone Revolutionary standing in their way. Luffy's other brother Sabo, having just eaten the Flame-Flame Devil Fruit that previously belonged to their brother Ace, is enough to hold back the entire Marine task force.
It doesn't seem like Fujitora was trying to hard to get past Sabo and vise versa. I mean look at the damage the other admirals have done.
Happens at the end of One Piece Film: Z, with the titular character holding off a battalion of Marines led by multiple Vice Admirals and Admiral Kizaru so the others can escape.
A villainous one is attempted by Charlotte Oven, one of the stronger Big Mom pirates, who tries to hold back the Firetank Pirates' amphibious ship when it's trying to escape. Unfortunately for Oven, it just runs him over.
Happened to Jubei in Yaiba during their quest for the Orb of the Dragon God, taking down thousands of mummies with him.
Maggie does this to hold back Wong in the climax of the Dokusensha arc of R.O.D the TV. She even cuts down a bridge to cause him to fall down. You'd think she'd have read The Lord of the Rings and be expecting the paper whip slap up to pull her down after him.
Atori from Noein, who uses his body to block the portal through which the forces of Shangri'La are attempting to invade.
In Digimon Frontier Sorcerymon does this to hold off the bad guys giving the kids just enough time to escape.
Team Rocket of has an impressive one in the Pokémon: Advanced episode "A Poached Ego." In it, they go up against a Tyranitar — BAREHANDED — in order to give their Arbok and Weezing a chance to escape into the wild with a herd of Ekans and Koffing.
Pokémon: Mewtwo Returns: Misty, Brock and the superclones face off Giovanni so Ash can deliver Mewtwo to the spring. We sadly don't get to see the battle ever start.
Subverted in Berserk. When Guts and Casca are separated from the Band of the Hawk and surrounded by 100 enemy mercs, Guts tells Casca to run and bring back help while he deals with them. Everything about this scene would suggest a heroic sacrifice, and Casca knows it, but can do nothing but try to get back with help as fast as she can. When she does arrive with the rest of the band, all they can hope for is that somehow Guts has managed to hold on, and it's a slim hope at best. And then they arrive, and to their utter shock see 100 corpses on the ground, and a wounded Guts passed out against a tree.
Even though Shoichi Irie from Katekyō Hitman Reborn! wasn't one of the good guys at the time, he really put up a fight against Tsuna when Tsuna is on the way to the laboratory. Some traps on the side and the final obstacle of the strange-eyebrow Genkishi was tough enough for Tsuna, but Shoichi attempt to stop Tsuna failed. They forgave each other later and became best friends by the end of the arc. :-)
Gundam has a couple of notable examples of this trope, only that it is the antagonists who are doing it:
The sight of Dozle fighting even with only a rifle was enough to make his delayed last stand surprisingly effective, and would of lasted if the Big Zam didn't blow up from under him!
The 08th MS Team OVA featured a pair of such instances (although the alignment of the antagonists is quite debated due to the show's Grey and Gray Morality): first with a few members of a squad sacrificing themselves to save the rest, and then with Norris Packard sacrificing himself to give the Kergeren time to escape. Unfortunately, both of them end up as Senseless Sacrifices thanks to the Federation's General Ripper.
In The Legend of the Legendary Heroes, when Tiir begins to massacre his troops and manages to severely injure him, Claugh orders his troops to retreat, intending to "hold him off as long as [he] can" to cover their escape. However, out of loyalty to their commander, they refuse and cover his retreat, with another soldier picking him up and carrying him away against his wishes.
Subverted in episode 36. After Ganju grabs Hanataro and escapes, Ichigo tells Kenpachi Zaraki that he can't let him pass through to pursue them. Kenpachi tells him that he's not interested in the others: he's just there to fight Ichigo. And what a battle it is.
In Episode 54, Ichigo faces off against three Soul Reaper lieutenants and Captain Kuchiki so Renji can get away with Rukia.
In Episode 154, the Arrancar Dordonii repays a debt of honor to Ichigo by fighting Rudbornn Chelute and the Exequias to give Ichigo and Nel time to escape.
In Episode 319, Yoruichi holds off the Reigei so Ichigo and Rukia can escape through the Senkaimon gate.
In Chapter 585, Renji, Rukia, Byakuya, Ikkaku Madarame, Yumichika Ayasegawa, and Shuhei Hisagi take on the eight Sternritter that had surrounded Ichigo in order to let him chase after Juha Bach, saying, "We won't let you pass." When someone tries to break through in the next chapter, they repeat the point.
Tien does it against Semi-Perfect Cell in Dragon Ball Z by spamming his life-draining Neo Tri-Beam to allow Android 18 to escape and therefore prevent the seemingly unstoppable Cell from achieving his perfect form. The attacks didn't hurt Cell (who was probably thousands of times more powerful than Tien), but they kept him pinned down, and considering that Tien had been Overshadowed by Awesome, it was both very unexpected and very Awesome. Cell was going to kill him for his interference, but Goku intervened.
Vegeta delivers an epic one to Majin Buu when he willingly kills himself trying to take the pink blob down with him. He does this all for the purpose of saving his son's life, knowing he would go to Hell afterwards for all of the terrible things he had done in his life. By placing himself right between Majin Buu and his son, Vegeta gives Piccolo just enough time to move Trunks and Goten out of the danger zone.
This happens near the end of Minagoroshi-Hen in Higurashi: When They Cry. Like, three times in a row. First Mion, then Rena, and then Shion.
Kimblee of all people pulls this in Fullmetal Alchemist. Just as Pride begins consuming Ed's body, Kimblee emerges from the maelstrom of souls within Pride and gives him a verbal lashing for being so cowardly. His interference delays Pride long enough that Ed was able to defeat him.
Greedling holding the line against the soldiers in Central also counts.
Eyeshield 21 plays this straight with Banba. It was due to his efforts that his quarterback is the first (and only) quarterback to survive the onslaught from the beastly Gaou.
Senji does this in the end of Chapter 47 of Deadman Wonderlandto prevent Hagire from overriding Ganta's memories to live on in his body.
"My apologies, but this passage is closed."
In Mai-Otome, when Shizuru and Natsuki lose their access to their Otome powers during Nagi's coup, Shizuru, over Natsuki's objections, decides to hold off the invading forces herself while Natsuki escapes to gather help to reclaim Windbloom and Garderobe.
How Jolyne dies in JoJo's Bizarre AdventurePart 6 - After roping Emporio to a dolphin, she holds off Pucci just long enough for Emporio to travel out of Pucci's reach.
Kikuchiyo from Samurai 7 hits this trope on the head in the final episode, when he stops a battleship. It becomes a Heroic Sacrifice, made all the more Badass by the fact that after the battle his boots are left firmly planted into the ground.
Yu Gi Oh Zexal has various allies pull this against the Seven Barian Emperors in order to protect Yuma.
In the final episode of Girls und Panzer, Miho is leading Maho further into the city, aiming to face her one on one. Naturally, Maho is followed by every single remaining Kuromorimine tank, save those distracted by Duck. She reaches her target and lures Maho in. Maho's team is on the verge of flooding in after her, when Leopon moves their Tiger(P) across the entrance and opens fire. What follows, albeit mostly off-screen, is the Porsche tanking round after round from several late-war German tanks and tank destroyers and absolutely refusing to budge or move a fraction of an inch from the entrance of the Nishizumis' makeshift arena. When it does go down, it goes down firing, taking a number of enemy tanks with it, and the Automobile Club having nothing to say to their adversaries but lighthearted taunts. note Bonus point for Leopon team for having angled their hull to improve armor deflection and for taking the tanks to their left and right first to use them as cover, both things showing they were notMistaken for Badass.
Followed by the Crowning Moment of Funny when their adversaries realized that immobilized Tiger at the chokepoint is still nigh impassable.
The Tale of the Princess Kaguya: Kaguya's father enlists the entire household to shoot down the Moon delegation as they arrive. However, the arrows turn to flowers midair, and everyone falls asleep save Kaguya's parents.
In Tokyo Ghoul, this is done by Ryouko Fueguchi to allow her daughter to escape when they're both cornered by Doves.