And I Must Scream/Web Comics

The Dragon Doctors brings us the story of Rina, who was Taken for Granite and left for two thousand years in a cave with nobody to talk to and no sensation at all (thankfully, she was only conscious for the first days). Fortunately the eponymous doctors rescued her. The comic also features Tanica, who was accidentally turned into a tree by Sarin. She can communicate with the others through magic, though.
- It's later revealed that a government did this to people who broke their no bodily alterations rule, just in case those people were ever needed. How useful those people would be after years, decades, even centuries as statues is questionable at best.
In Drowtales, Kharla'ggen of the V'loz'ress clan has a creepy hobby when it comes to dealing with those who catch her fancy or resist. Using surgery to remove the bones in their arms and legs, along with their teeth, eyes, tongue, hair and fingers (sometimes their ears too), turning them into living dolls.
In the completed sprite comic In Wily's Defense, Dr. Gabriel Knight was killed in a lab accident, but his soul survived in one of his incomplete robots through some divine intervention. The robot was kept frozen in stasis, unable to move or speak, but Gabriel could still see and hear everything happening in front of him. His wife, also a scientist specializing in robotics, disappeared for a year to mourn. Needless to say, Gabriel had completely lost his marbles by the time the robot was finished.
In Girl Genius, there is a plant that gives off a pheromones (or something) that induces feelings of extreme happiness, and then eats the prey (similar to a Venus Flytrap). Apparently, this plant takes over a year to fully absorb large (read: human-sized) prey. So far, Taverk and Zola have neglected to mention exactly how quickly death comes for a victim.
This almost happened in The Gods of Arr-Kelaan, but the goddess of death personally intervened.
A manga link. It's from the artist who did the Idle Minds.
- Not quite over, for those of you who thought you'd escape sane. (The pictures to go with the first strip's ending narration.)
- Ian Samson is a big fan of illustrating "turned into an object" comics. He's done things like having the super-heroine Synthia Stretch trapped forever as a bouncy ball toy. A girl with clay-based shapeshifting powers losing her ability to control her form and being turned permanently into a clay urn. And possibly most disturbing, a girl who's witch sister has ruined her life by constantly turning her into various articles of clothing. The witch eventually assumes that because she has no friends and no social life, she must prefer being an object, and decides to stop turning her back into a human. Unable to complain, seeing as how clothes don't have vocal cords, her sister spends the rest of her life trapped as one article of clothing after another.
- Being one of his works, City of Reality deals with a lot of this. Magic World is full of people who, thanks to Hinto Ama, have been transformed into all manner of things, from turtles to clothing to water. At least there's the Manumitor, who goes around saving as many of these victims as he can.
  - In fact, in this work, the trope seems slightly subverted as usually the author's works seem to heavily imply that a person will be stuck forever. In City of Reality, it is mostly heavily implied everything will be okay eventually.
Jack by David Hopkins has a short story about a guy who gets offered a very nice apartment for free, ostensibly so he can convince other prospective buyers. Things get increasingly weird, and it turns out he can't leave. He demands to know where he really is, even though he's warned that he won't be able to come back to this paradise... turns out he's in a particularly unpleasant part of Hell. And he stays there.
- Jack is full of this - It's in large parts about Hell, after all.
In Namesake Selva, the Wicked Witch of the East turned the Munchkin King into a hat box and Selva herself is turned into a purse
The NSFW webcomic Oglaf couples this trope with Fridge Horror in this strip.
In Sluggy Freelance Jane, who's got the "you can live forever, but your body can still decay" kind of immortality. She eventually becomes simply Zombie-Head-On-A-Stick, a barely articulate head-without-a-body, filled with an all-consuming hunger she can never satisfy, and doomed to be the plaything of bored idiots. However, at least she's eventually decay away completely if she doesn't satisfy her hunger for brains... it'll just take a very long time.
- While Jane's fate is played for laughs and she might not even mind her new existence so much in the end (it's not really evident), a version happens to another much more sympathetic character without any especially magical or scifistic means: Kept alive indefinitely by advanced medical technology but too hurt to be healed or for the pain to even stop, suffering from the same extreme agony permanently whenever conscious. It makes the "must scream" part literal.
This sort of thing happens way too much on The Wotch. Scott has been transformed into an immobile, conscious statue three times so far, though it didn't last very long. Rosetta wasn't so lucky, as she got turned into a statue by a crazy wizard, kept that way for some time, then released following said wizard's Heel Face Turn -- only to be turned back into a statue by a basilisk without anyone knowing what happened to her. It's been mentioned that some statues in museums and mannequins in department stores are transformed people. And some people consider this a humorous comic.
- This also almost happened to a demon early in the comic's run...before the Big Bad and The Dragon rescued him.
In The Zombie Hunters, the Basilisk zombie possesses an automatically paralysing bioluminescent gaze. Any human that locks eyes with a Basilisk will suffer a painful seizure and become immobilized. The victim then has no choice but to lie there helplessly as the zombie closes the distance to feed. Slowly. Starting with the face.
Start Of Darkness, one of the prequels to Order of the Stick, initially plays this straight, when Xykon traps the soul of Lirian the druid in a magic gem, raises her corpse as a zombie, and threatens to feed the zombie to an ogre, thinking that it will drive her insane. Later subverted when he traps the soul of her lover Dorukan in the same gem. Because Evil Cannot Comprehend Good, he accidently creates a You Are Worth Hell situation instead.
Sarda from 8-Bit Theater went back to the beginning of the universe, and is forced to live through every major event in the universe over a period of billions... no, TRILLIONS of years. He admitted that the only thing keeping him alive at that point was pure, unadulterated hatred of the Light Warriors.
The Helmsman from Homestuck. Formerly the Ψiioniic, ancestor of Sollux and follower of The Signless, he was captured by Her Imperial Condescension when the Signless' rebellion failed. She extended his lifespan indefinitely with her magic, lashed him to her spaceship, and used him as a living battery to massively overclock her ships power. He exists in a state of undying, perpetual agony for thousands of years before he is killed by The Vast Glub.
In Verlore Geleentheid Jane Onoda was in cryogenic stasis for ten thousand years but due to a computer glitch she and the others on her ship were conscious the whole time. The only reason she stayed (somewhat) sane is that the ship's computer kept her occupied with battle scenarios against the species that nuked her homeworld.
Nedroid: Described in the Alt Text of this comic:

"It grows from here. Reginald begins reducing more and more actions to simple lines of dialogue: "nod", "dance", "laugh", "love". Eventually his muscles atrophy; his body wastes away. Only the left hemisphere of his brain remains alive, the spoken word itself reduced to mere thought. And once Beartato earns his master's degree and invents a brain-to-speech synthesizer, that final thought is at last heard: "Weep a single tear for the life I have wasted".

Goblins reveals the terrible nature of Kore's curse in Book 7: all his victims' souls are trapped in his body and suffer endless torture, a few days felling like several years. And he has been cursed for a good thousand years!