Several of Narutaru's most horrific scenes fall under this. The most infamous examples include the test tube incident, the victim of said attack getting her bloody revenge on the main perpetrator by siccing her own torture methods onto her via her newly-acquired Shadow Dragon, and the utterly brutal rape and murder of Norio in the manga.
Bokurano by Mohiro Kitoh has a guy getting half his hand sliced off, in detail. In the manga, there's also the scene where Chizu slits Kako's throat.
Marco's corpse is pretty horrifying, and the titan puke full of dead bodies in the same chapter is just disgusting.
The Mazinger sagas, being made by Go Nagai, have of course plenty of this, although compared with other works such like Devilman, Nagai toned it down:
Mazinger Z: In one of the first manga chapters, Kouji knocked an Iron Mask's helmet down during a fight, and then he saw his brain was visible underneath (and tubes and circuitry sticking out of the brain matter). Shortly after, when that Iron Mask attacked him, Kouji accidentally slit his throat, and a gush of blood splashed him.
Later, when he was fighting the Gamiasisters, he chopped them into pieces. They were so human-like they bled as he did so, and their remains lying on the floor seemed several dismembered, blood-stained humans corpses (as Kouji noted, trying not retching).
Great Mazinger: One of the manga versions gave us a delightful pannel where Marquisse Janus sliced secondary character Misato in two halves lenghtwise with one single nail of her Humongous Mecha.
UFO Robo Grendizer: The scenes of the Fleedian genocide in the manga. Other than the visions of charred corpses, there are a particularly brutal flashback where one of the Vegan commanders let drop several hundred of people (including children) from several thousands of meters of height. Some panels showed heads of people splattering upon hiting the ground. theHero Duke Fleed described the scene as "a deluge of children falling from the sky".
Shin Mazinger Zero: Where do we begin? In the first arc you have Kouji getting his arm ripped from him, and Sayaka getting raped and then impaled with several dozens of metal rods. In the next arc, the Gamia triplets shredded two guards in thin ribbons. Shortly after one of them got shredded, another got shot through her skull and then sliced in half, and the third got cut in half when she tried to run away...
Orochimaru's fight with four-tailed Naruto where he sheds his body like a snake skin, and makes a copy of himself, by gagging one out of his mouth.
Kimimaro's Kekkai Genkai that lets him tear out his own bones to use as weapons: even more so in the manga, because his fingers split in half so he can fling the bones like bullets, pulling his spine out of his back and uses it as a sword, and other things.
Shino and the other members of his clan are human insect hives. Made worse when the Fridge Horror hits you that, with the expendable manner the insects are in use and their short lifespan, they have to be continuously mating inside his body (this is actually made explicit in the anime and he even has a technique where he makes them mate faster).
Peacemaker Kurogane has Suzu carrying around his masters head in the last episode which eventually decays into a skull. As well as a good number of the battles towards the end.
Berserk is a Nausea Oil Refinery, with plenty of goriness and Fan Disservice to go around. The horrors of the Eclipse from Volume 13, for example. For a specific example, the scene where Slan manifests herself to Guts using the intestines of dozens of dead trolls to form her body.
In the TV series, there's Luke Valentine's demise, wherein he is eaten alive by Alucard's hellhound familiar. While the worst of it is never shown, it's the sound effects that turn the stomach.
In the second OVA, the audience sees Luke get devoured with body parts and limbs flying everywhere (which are then eaten) and gallons of blood decorating the walls. For bonus points, it's played up for all its horror and Nightmare Fuel.
Rip Van Winkle's death in the fourth OVA.
Seras (as a child) helplessly watching her mother's corpse being raped, and Zorin's death in the seventh OVA.
The scenes where Mima is being photographed naked.
The corpses that have their eyes gouged out.
The photographer being stabbed in his eye, his crotch and then repeatedly stabbed over and over by the supposed "pizza deliverer".
Me-Mania's physical appearance and his attempted rape of Mima.
The final battle between Rumi and Mima.
Tokyo Tribe 2: "Goosh Goosh". It's so bad there are reaction videos of it. It features Buppa, a Fat Bastard crimelord, raping a truly unfortunate Bishonen to death, and all the while the guy is doing this, he keeps saying GOOSH GOOSH! GOOSH GOOSH!
Several bits in Neon Genesis Evangelion like the Bardiel fight, which ends with the Angel's viscera splattered over a town and several mountains. Kaworu's death, where his body is crushed and his head blown off from the pressure. And the part where Eva Unit-1 defeats Zeruel and then eats it.
There's also everything in The End of Evangelion. Especially the way Asuka checks out, getting ripped to shreds and Eaten Alive by the Mass Production EVAs.
New Getter Robo has an astounding number of shots of fat pilot Benkei's hairy/warty ass and testicles, for a 13 episode series.
The beginning of the first episode, Lucy's various other murders throughout the series, what happened to Mayu, and Bandou's fights. The man gets an arm cut off, another one broken, and his eyes forced through their sockets by Lucy.
The cruel kids from Lucy's childhood who kicked the puppy she had been caring for against a wall and beat it to death with a vase as they forced Lucy to watch in horror. And then, shesnapped.
School Days: The ending of the anime. Sekai stabbing Makoto causing Makoto to make gurgling noises, his eyes to bulge out of his head, and ends with him lying in his blood. Later, Kotonoha is revealed to have cut off Makoto's head and carries it around with her in a duffle bag. Then she stabs Sekai, which releases a torrent of blood, and cuts into her stomach so she can look for the baby inside. Finding none, she stands up, covered in Sekai's blood and we are treated to a inside looking out shot of Sekai's stomach. The final scene features Kotonoha lying on her family's boat, and holding Makoto's head close to herself with an expression of absolute bliss on her face. It's much, much worse on DVD where the blood is red and everything.
The Fingore in Monster. The fat, ugly hooker talking about Roberto's large penis.
The scene in the first episode of Haibane Renmei where Rakka's wings develop to full size in a matter of seconds. Includes all the blood and gory stuff you'd expect when two new appendages suddenly grow out of someone's back.
Hiromu Arakawa's masterpiece Fullmetal Alchemist has quite some notorious examples, including the thing that the Elric brothers created when attempting to resurrect their mother. Her earlier work Stray Dog has some minor examples restricted to a few pages, but those present are profoundly disturbing; that is, unless human remains and vivisection related imagery is your thing.
Hänsel and Gretel from Black Lagoon. They slaughter everyone they can because they can, sacrifice children to get out afterward, play some really sick games with the survivors of their assaults and are smiling the whole time. Them being probably incestuous is likely their least disturbing attribute.
Author of Black Butler Yana Toboso certainly seems to enjoy the gory side of life, what with the orphan murder rituals, vomit covered Ciel clinging to Sebastian and, in the second series of the anime, Alois Trancy trying to gouge his maid's eye out at the breakfast table for kicks. Plus the sword they keep in Hannah's esophagus.
There's an element of Nausea Fuel in anything by Junji Ito, but the short story Glyceride, the part in Uzumaki where they eat the snail-people, and the whole kidney arc of Tomie in particular. Also, the additional Tomie story in Museum of Terror where her ex-lover continually beats her constantly regenerating body to a pulp, and then disposes of said pulp by turning it into sake.
When Sen has to bathe the muck spirit, but worse is when No-Face is purging himself.
The early scene where the parents transform into pigs is pretty repulsive.
The scene in the manga of Tactics in which we see Kantarou as a child, taking a shit, and we get a good view of the turd coming out. Whoever thought it was a good idea to show that must be one sick person.
Mami being eaten alive by Charlotte. In the anime you don't see it, but you hear it. In the manga, you see it all.
In the prequel Oriko Magica, Kazuko-sensei is the one who gets chomped on. It's just as ugly.
The animated adaption of Fate/Zero gives us Zouken's...welcome to Sakura via insect-rape. She's a girl of like 5, and you get to see the aftermath in glorious high definition. He also implies that he raped her on the first day she was here - which, those who played Heaven's Feel in Fate/stay night know to be true. Not only does it make you want to throw up, it does absolute wonders towards your hatred of Zouken.
Panty & Stocking with Garterbelt. Monsters in the beginning of the series always were some sort of personified Nausea Fuel. A shit monster, sperm ghosts who died during masturbation, a bulimia monster who had boobs for eyes, the vomit monster that causes others to retch all over Tokyo...
In Magical Record Lyrical Nanoha Force, the blobs of bone-like flesh that are seen are what happens when a person gets in contact with the Eclipse virus and fails to be compatible with it. Looking at it is just... eugh. Doubles as Nightmare Fuel.
In Toriko, Toriko has his arm bitten off, and you get to see what a severed limb looks like, blood spurting out and everything. This was smoke censored in the anime.
Ragyo Kiryuin's "treatment" of her progeny is NOT a way a parent should raise their child. This is most notable when she molests Satsuki.
Junketsu being grafted onto Ryuko's body so she can't take it off and her ripping it off with her bare hands, with High-Pressure Blood ensuing.
Kamui uniforms derive their power from the blood of their users. Viewers who are Afraid of Needles and have experienced having their blood drawn may feel themselves fainting at the whole concept.
Sukuyo's mystery croquettes. In the first scene they're shown, the worms in the croquettes seem to move.
The entirety of episode 12, after Ryuko overwhelms Senketsu with her rage and they morph into a hideously deformed berserk hybrid. There's blood spraying literally everywhere, Ryuko and Senketsu are both screaming in savage agony, and the extent of the damage they take before they finally go down is almost sickening.
The end of episode 18, where Ragyo rips Ryuko's heart straight out of her chest, still connected and beating! And then episode 19 ups the ante when Ragyo holds an entire conversation with Ryuko while still holding the beating heart; when Ryuko finally gets out of Ragyo's grip, her heart is briefly seen dangling by its arteries before being sucked back in her chest, as Ryuko is looking in pure horror at just how inhuman her body is. This is repeated in episode 20, with Nui holding out her own heart, colored a rather unhealthy-looking blue, but it luckily has less focus.
Episode 24 has Ragyo ripping out her own heart and crushing it in her bare fist, all in glorious, nauseous detail.