In Fullmetal Alchemist one can became this, if a person attaches someone's soul to a suit of armor with a blood seal.
Alphonse Elric is one of these. Different in that he's a main character, and a good guy. Also, the fact that he has the voice of an eleven-year-old takes a lot of the intimidation factor right out.
Both Al and Ed fight empty suits of armor at one point. They're not quite as nice; both suits are controlled by serial killers. Then again one turns out to be Affably Evilas well as being two people. The other turns out to be Barry the Chopper. Barry turns out to be fairly good-hearted, though still loving to kill, until he is irrevocably killed.
There are also the mass-produced suits of armor Hohenheim created for the Thule Society in The Movie of the 2003 anime version. Though they have people inside them, they've been killed by the intense cosmic forces inside the portal that connects the FMA-verse to the real world & the armors are animated by the forces that dwell within the gate. Taken to a slightly creepy level when Al takes control of one (which just happens to look like his old self) and uses it to help him fight the others, then after they get recalled, temporarily mind-rides back to our world with it.
In the Ronin Warriors OVA Gaiden the Armor of Halo is seen running around the streets of New York without its owner. Turns out it is being controlled by Shikaisen the Big Bad of the story. The Armor of Torrent is seen walking on its own in the last episode of the OVA Legend of the Inferno Armor in order to join the other Ronin armors that were captured by Mukala. It has been confirmed by the main characters that the armors can be used for good or evil. But the more fights the armors are used in, especially without the human spirit, the more corrupt the armors become. That is why by the end of the second OVA the armors are destroyed for good.
In Saint Seiya, both Gold Saints of Gemini have used their armour to defend their temple without actually having to be there or wearing it. Shiryu overcomes the first instance of this quite effectively.
Also, in Saga's epic hallucination/dream/vision/omen of doom sequence during the Sanctuary Arc, all of the 12 Gold Cloths and the five Bronze Cloths currently making plot are seen to be what would pass as empty but moving-if it weren't for the eyes. Whatever happens, they turn on Saga.
In Slayers Evolution-R the cast meets one of these when they begin their search for the Hellmaster's Jar. This armor is in fact possessed by the soul of Naga the Serpent, who had a run-in with another cursed jar. In the process Naga lost her memories and began referring to herself as Nama.
In The same story arc they help a squad of animated armors recover the Helmet of one of their members.
In the OVA "Jeoffory's Knighthood", the Big Bad uses a legion of these guys as his Mooks.
Seen in an episode of Space Adventure Cobra: while on a desert planet, Cobra and Lady are confronted to what appears to be animated empty suits of armor. They are in fact a species of telekinetic or haunted swords controlling the humanoid armors to move around.
In Berserk, there's one of at least lich level. Formerly a king with too much a fancy armor.
In Pokémon Best Wishes, an episode had a Yamask haunting a museum, going as far as having a suit of armor attack the gang. Similarly, another episode has a group of Litwick scare the gang by using Psychic and making a bunch of objects form a makeshift golem, such as a statue bust for a head, an umbrella for a sword, etc.
Not really armor but the uniform from Kill la kill, it does become armor though
in Zatchbell, one of the mamodo's powers is to control things with flowers, one of the defenses guarding the castle where they fight is a Zerg Rush of empty armour suits controlled by these flowers.
The Destroyer from The Mighty Thor has been described as such, but is quite a deconstruction of the idea: The Destroyer armor is physically empty and only moves when animated by the Life Energy of a person using it, willingly or not.
The same goes for the Destroyer in the film, with the added coolness of being able to reverse its entire body. And energy blasts.
Iron Man's armors are sometimes remote-controlled. And sometimes, like in Hypervelocity or the Tony's Abusive Boyfriend arc, it has its own AI, which can impersonate him and speak. Special mention goes to the Safe Armor, which was partially infected by Ultron and became yandere for Tony.
Conan the Barbarian once fought one of these guys, realising he was screwed as even though he could chop the arm and the head of the armor off, the thing could still attack. Thankfully the Wench of the Week shone some light into the priest controlling it, following which it collapsed like a sack of potatoes.
The Destroyer in Thor. Its arrival to Earth includes this lovely Shout-Out.
Agent Sitwell: Is that one of Stark's? Agent Coulson: I don't know. Guy never tells me anything.
Iron Man 3: The Mark 42 armor can be piloted remotely by Tony or controlled sans pilot by J.A.R.V.I.S. The same applies to all of Tony's other armors, which he summons to fight off the Mooks in the climax.
The Witch-King in Lord of the Rings is a spirit that is incorporeal when not clad in something, like the rest of the Nazgűl, but when he rides into battle in Return of the King, he becomes something between this trope and Tin Tyrant. Cue the clattering armor falling on the ground when Éowyn and Merry kill him.
Referenced by Puddleglum in C. S. Lewis's The Silver Chair. When the protagonists first encounter the Lady of the Green Kirtle, she is accompanied by a knight in Black Armor. Puddleglum posits that while the armor is certainly man-shaped, the wearer might not be a man. Among the possibilities he lists are "A skeleton" and "Nothing at all." Jill and Eustace are understandably spooked.
Almost every Marine of the Thousand Son are like this, having their bodies turned to dust.
In Voyage of the Shadowmoon by Sean McMullen, Silverdeath is a chainmail vest that, once put on a "host", transforms around them into a full suit of armor capable of scouring entire continents of life; this is essentially animate armor since the host has no control over what Silverdeath does.
The animated armor army from Bedknobs and Broomsticks.
McGonagall and Flitwick enchant the armour of the castle to fight in the Final Battle of Harry Potter and the Deathly Hallows. This was hinted at in various places in the earlier books, if you paid attention (they occasionally moved on their own, and could even be taught Christmas carols).
Lancelot fights against an animated suit of armor in the Roger Zelazny short story "The Last Defender of Camelot".
Sort of subverted and played straight at the same time in the Culture novel Matter. Some characters lack the training and reflexes to use the Culture's combat suits in a fight, so their targeting and evasion systems are slaved to the onboard computers.
In the Warhammer novel series following Konrad, the eponymous hero encounters a knight clad in bronze plate, and upon defeating him finds the armour empty. Being too Genre Blind to realise that this is the Wahammer Old World, he takes it for his own, and finds that it is magically aiding him in battle. And then it takes control of his movements. And starts eating him.
In the first book in the Deltora Quest series, Leif and company run across the villainous Gorl. Upon his defeat, they discover that his centuries-long stand as guardian of some magic flowers has long since reduced his body to dust, leaving him as an empty suit of armor animated by sheer undying willpower.
Live Action TV
Kolchak: The Night Stalker episode "The Knightly Murders". The ghost of an evil knight animates his old suit of armor to kill everyone responsible for the desecration of his burial site.
Failed pilot Lost In Oz had these, enchanted by the Good Witch of the South.
The Forgotten Realms setting had Animated Armor constructs created by magic called Helmed Horrors and Battle Horrors. Typically used as guardians, especially in isolated places. Also, a rare wizard spell "Iron Maiden" creates short-living, but fully powered and undispellable Battle Horror.
Subverted several times in module I6 Ravenloft. In a spooky Gothic setting, the Player Characters repeatedly come across empty suits of armor that they may expect to attack them. Most of the armor suits do nothing: one is rigged to spring forward and flail around, scaring the PCs but not seriously harming them.
Module S4 The Lost Caverns of Tsojcanth. One room has three sets of empty, magically animated suits of armor. In order to escape a PC must defeat a set of armor and put on its helmet.
The Rubric Marines of the Thousand Sons in Warhammer 40,000. Notable in that they are suits of futuristic powered armour, but animated by magic and the ghosts of their former occupants in the manner of the traditional fantasy version. The interesting juxtaposition of sci-fi and fantasy tropes is a big part of 40k's charm.
And the Eldar Phoenix Lords who are no longer alive and have become amalgamations of souls controlling ancient battle-suits.
The Necrons are essentially an entire alien race of this. Their souls are bound to regenerative robot bodies. But after millions of years, this has left most of them insane or as unthinking automatons.
According to the backstory of the Legendary Six Samurai in Yu-Gi-Oh!, Shinai was most trusted by Shi En as a heroic warrior who could escape from the jaws of death, no matter what. However, after sadly dying in the later years of the great war, his soul ended up dwelling inside the armor he died in, and now protects the current generation of the Six Samurai.
Hakumen from BlazBlue counts. His soul is confined to the Susanooh unit, the armour that covers his body.
In Lords of Shadow, they finally explain how they work (giant suits of armor possessed and animated by poltergeists). After ripping off their shield, you kill them for good by prying open the breastplate, grabbing the spirit inside, ripping it out of the armor, and crushing it.
In Dragon Quest V, Restless Armours are one of the recruitable Mons, and can be found as an equippable (and cursed) armor.
Gotcha Force has the Ghost and Elemental Knights. However, it's quite obvious that they're empty, as they have no helmets and the latter's armor even falls to pieces when it throws its sword (which contains its lifeforce).
The Guard Armor/Opposite Armor, the second boss of Kingdom Hearts. Hard to say whether it's exactly empty, but it certainly doesn't have a person in it. The same creature shows up again in 358/2 Days; from the looks of it, it seems more like it actually is the armour, rather than something controlling it. Considering that it has Raymanian Limbs, and the ability to fire energy shots when it turns into the Opposite Armor, that should have been a no-brainer.
Any Keyblade wielder with a strong enough will can apparently leave their armor behind as a sentiment, BBS Final Mix has the Armor of the Master and No Heart, the sentiments of Eraqus and Xehanort, respectively.
Guild Wars has a few enemies like this. The Forgotten and Mursaat use animated armor for their melee units.
In the first Legacy of Kain, Malek of the Sarafan. Also his minions in his castle.
The Legend of Zelda: Phantom Hourglass has the central dungeon being patrolled by suits of armor called Phantoms, who are completely invincible (at least, until you get the Phantom Sword). If one of these scores a hit on you, you lose a full heart, 30 seconds off of the titular hourglass, and are sent back to the start of the floor. They come in three flavors: regular(blue), fast(red), and teleporting(gold).
Special mention has to go to The Legend of Zelda: Spirit Tracks, where Phantoms controlled by the ghost of Princess Zelda, whose soul is separated from her body in the first hour of the game, can be used to help out in dungeons. However, while she isn't controlling it, it acts just like those in Phantom Hourglass. It's worth noticing that while she is in control, you can speak with other Phantoms... who give stereotypical office chatter. (There's a reason why this game is considered the most tongue-in-cheek of the franchise.)
Iron Knuckles, an uncommon Boss in Mook Clothing, are usually walking suits of armor (sometimes with people inside them, sometimes not).
In Fire Emblem: Path of Radiance, Ike and Soren discuss this trope and rumours concerning it. Soren mentions that there's a rumor that the Black Knight isn't actually a man inside the famous suit of armor, but that it's possessed by a demon or similar. Though they quickly dismiss the possibility, it does turn out there's something not right about the man.
Some enemies in the first level of MediEvil 2 are emerald-colored suits of armor.
Some suits of armor in Resident Evil 4 will strike at the player when they come into range, and fall into pieces after the attack. Apparently these suits are infested with Las Plagas. Leon also has to fight more mobile and resilient Armadura, blowing off their helmet and destroying the parasite inside before they go down. As with all Las Plagas, the parasite dissolves to nothing after death.
The armor may be a remnant of an earlier incarnation of RE 4, which had a more supernatural flair. In it, Leon is investigating Umbrella's European HQ mansion. Haunted dolls, spectral fires, animated armor... it's very much the haunted house. Supposedly, it was dropped as being TOO paranormal, and thus, too far away from the RE mold.
And became the original "Devil May Cry".
In RuneScape there is a Warriors guild when one can bring a set of normal armour to animate it and fight against it as training.
Vagrant Story's Dullahan, Last Crusader, Nightstalker, and Dark Crusader are all suits of armor that Lea Monde has infused with the power of the Dark. Some are sent to bar Ashley's way by Sydney himself; others are reanimated by the Knights of the Cross.
Bishamon from Darkstalkers is a suit of samurai armor possessed by an evil spirit.
The Demigod Oak is an empty suit of armor inhabited by its former wearer.
A notable subversion in Fable II in Terry Cotter's. Befitting the name you find an army of suits of armor. Many would tell you this is where they start destroying the armors in case they attack. They don't.
Warcraft III has the War Golems, which are golems made from a giant suit of armor.
The same game, as well as World of Warcraft, also has Revenants. Those are sort of elementalundead which manifest as a floating suit of armor controlled by an elemental force. In Warcraft III there were few physical differences between them, all appearing as the same armor (of different sizes depending on the revenant's power) held together by a vague flowing energy (usually blueish for both Ice, Frost and Death revenants, though Fire ones have orange energy.) World of Warcraft gives different types distinct armors, and their elemental affiliation is more clearly defined with mud, water, fire or wind swirling inside the armor.
Final Fantasy X and X-2 have an entire class of enemies devoted to this. The only problem is the fact that these suits are at least 15 feet tall. And thus outclass you when you first come across them. Completely outclass you.
Dragon Age: Origins had a quest where, if you went in a certain room that was filled with suits of armor, their heads would follow you, and if you got to a certain point, they would attack you.
Desktop Dungeons has Animated Armor in the Factory special dungeon. They only have one hit point, but they all have a number of Protections From Death (the ability to survive one fatal blow) equal to their level. This makes them really useful for level-springboarding, since they don't regenerate the "hits" if you run off to heal. Find one you can survive one hit from, attack it, retreat until you heal and repeat until it dies.
MOTHER 3 features these as enemies confronted by Duster during his "infiltration" of Osohe Castle.
The Battle Horrors and their weaker cousins the Helmed Horrors in the first Baldur's Gate.
One of the new families introduced in Pokémon Black and White, Golett and Golurk (particularly the latter), are golems resembling armor suits inhabited by spirits, giving them an unusual Ground/Ghost typing.
If one considers an arthropod's exoskeleton to be armor then Shedinja also counts. It's the empty exoskeleton left from Nincada evolving into Ninjask and is a Ghost/Bug type with 1HP but an ability that makes it immune to any attack which is not super effective.
The Castle Realm in Gauntlet: Dark Legacy has animated suits of armor as enemies in the later levels.
Lost Kingdoms has the Ghost Armor and the Chaos Armor (which is an upgrade of the former). They are dullahans, they carry their heads (which are on fire), and they are fairly impractical to use. Both of them are upgraded from the Dragon Knight, though it's unclear if that creature counts as this trope or not.
The Black Knights in Dark Souls are Animated Armors that are all that remains of the knights that accompanied Lord Gwyn when he linked the First Flame. The kindled Flame reduced the knights' bodies to ash but breathed life into their armor. The Iron Golem is also a 40 feet tall armor suit animated by its "core".
The Trauma Harnesses in Fallout: New Vegas: Old World Blues were originally designed to take over the motor functions of injured soldiers and evacuate them from battle, but after the users died due to being trapped in the malfunctioning suits, the harnesses continued to operate autonomously, with skeletons still occupying them.
Found as common enemies in the mansions of Luigi's Mansion: Dark Moon. The early ones are invincible, the later ones can be tripped to reveal their possession by a ghost. The Tough Possessor boss also uses them as hosts, including a gigantic version.
In the Crysis series, this is Alcatraz's ultimate fate. His vital organs are all shot, so his suit starts to break his entire body down and turn it into more nanosuit mass. Thanks to Brain Uploading, no physical problems arise, only existential ones (which Prophet is happy to spend the entire third game whining about).
In Terraria, one of the enemies is the Possessed Armor.
In Code Lyoko episode "The Girl of the Dreams", XANA's specter takes control of a samurai armor owned by Yumi's family, which she brought to school for a presentation about Japan.
The Fright Knight from Danny Phantom is an arguable example; he's a ghost, so he doesn't really have a physical body of any kind, but his appearance is that of a suit of Black Knight armor with glowing eyes, and when he's defeated in his debut episode, it's shown crumbling away to reveal nothing inside.
Castle Captor has these patrolling inside it in The Smurfs episode "Lost Smurf".
Raytheon XOS 2exoskeleton is intended to be capable of autonomous action when it's finished, with the idea that a soldier can take it off, and send it ahead on remote control to a situation too dangerous for humans.
Leonardo da Vinci created a robot using a suit of armor that could sit, stand up, move its arms and raise its visor.