The Disembodied

In the world of fiction, life and death aren't always black and white, there's a very large and very varied grey area, one aspect of which is characters that aren't dead so much as corporally challenged. The Disembodied was once human but lost his body through a bizarre accident without actually dying.

See also Astral Projection. Compare with Ascend to a Higher Plane of Existence and Virtual Ghost.

Anime and Manga

 * Fullmetal Alchemist: Alphonse Elric lost his body due to botched attempt at human trasmutation and ended up as a soul stuck inside a suit of armour.

Comics

 * Hellboy: Johann Kraus was a German psychic whose body was destroyed due to a psychic disaster. His ectoplasmic form 'survived', but needs to be constantly contained to prevent it from dispersing.
 * The Legion of Super-Heroes' Wildfire, sort of like Johann Kraus, is a being of pure energy who needs to wear a suit to survive.
 * A minor student at the Xavier academy in the X-Men comics, Dummy, was also basically a suit with sentient gas inside of it.
 * Allen the Amorphous Cloud of Gas in Dilbert was so uncommitted that eventually the particles that make him up became bored and stopped binding. Now he exists only as a faint odour near the copy room.
 * A variation appears in Elf Quest. (big spoiler, because it happens late in the story)
 * Holocaust from Age of Apocalypse and Exiles.

Literature

 * In Perry Rhodan series, a man named Ernst Ellert was among the the first generation of known "mutants" (people with psychic powers) and was a member of the first Mutant Corps; his power was the ability to separate his mind (or astral body, or soul, whatever you want to call it) from his physical body and travel through time and space along temporal strands. He could travel to the past, or could select the statistically most probable future among several potential futures and follow the strand to see where it led. He died a heroic death in 1972 in an accident with high voltage, but the shock of dying completely separated his astral body from his body and he was hurled through time and space. After a long odyssey (during which he learned that his astral body could enter and control the bodies of physical beings), he eventually managed to return to 21st century Earth. For a short time, he was even forced to "possess" his own preserved dead body, until the deteriorating state of the body put it beyond his powers. In the year 4013, Ellert was given a new material body, created by advanced alien technology out of billions of sentient nanomachines. The new body was humanoid, although Ellert's control over the nanites allowed him to transform his body into a cloud of nanomachines and solidify it again at will, e.g. to walk through walls.
 * Voldemort in Harry Potter, following a backfired curse.
 * Happens a few times in Labyrinths of Echo - once to the powerful-yet-clueless protagonist, and in the sequels to a hapless victims of corporeality theft - they turn into ghosts without leaving bodies behind and technically this can be reversed. Also, novice Khumgat travelers tend to feel that they bodily don't exist (there's nowhere to exist), since it's more state of absense of space in the usual sense rather than a separate physical space - though upon re-entering a physical world the process reverses just as instantly and without noticeable aftereffects.

Live Action TV

 * General Zod in Smallville until the events of "Dominion".

Tabletop Games

 * Dungeons & Dragons has spells transmutating the target in this way - wraithform, gaseous form, shadow form, and several ways to transform (to various degrees) into an air elemental.
 * Forgotten Realms has a condition affecting wizards usually due to contact with wild magic and/or enchanting too many items in too little time, which may end in transformation to Wizshade - a ghost-like entity which gets sucked out of the crystal sphere into phlogiston. A wizshade doesn't age and temporarily returns now and then, but usually isn't lucid enough for meaningful conversation - so it just pops up in a colorful vortex, grandly babbles cryptic nonsense and/or randomly hurls spells, then vanishes again.

Video Games

 * In City of Heroes, Positron was a guy who was essentially converted completely into antimatter. He was stuck permanently inside his armor, and when it was damaged, he actually started leaking out. At one point, Badass Normal Manticore successfully scares off a whole group of powerful supervillains by threatening to put an arrow through Positron, turning the guy into an antimatter bomb. One of the comic storylines ended with Positron having a wish for a regular human body granted, with his character in-game changed to reflect this.

Web Comics

 * Bethan in Chirault became intangible after she ran afoul of a magical guardian and it was destroyed before finished to dissolve her body. Good think Bethan doesn't have to eat in this state, but it can be kind of humiliating - especially when you remember she used to be a warrior. Kiran asked a good (if not polite) question: "how do the clothes stay on?" The clothes became ghost-like too, but at least this got an answer to another question: it looks like she still can blush.