X-Force Volume 3: Reverend Craig treated his only daughter, Rahne Sinclair, as scum even before she turned out to be a mutant with a wolf-shifting power. This ultimately led to a situation where he brainwashed her into ripping the wings off of one her friends, then tried to shoot her. Seeing him in front of the wings he'd mounted as a trophy made her brainwashing kick back in, and she promptly ate him alive.
Comic/film example: Spider-Man. Spidey, infuriated over his girlfriend's death/near-death note depending on which version you're reading/watching , has the Green Goblin on the ropes when the villain reveals that he is Spider-Man's friend's father. As the Green Goblin apologizes, he sets up his glider behind our hero. Spidey jumps out of the way at the last second and the blade on the glider's tip impales the Goblin, killing him. For now.
In "Ultimate Iron Man", Howard Stark makes a point of preventing Tony from killing Loni note which is a little odd, since Tony has killed dozens of people by this point, but perhaps this is different since she's helpless and it would be cold-blooded murder rather than combat , only for Loni's son Obadiah to come do the deed himself. Countlessly averted in the same series, where Tony saves Obadiah from multiple near death experiences, to Obadiah's amazement. It's a case of Laser-Guided Karma too — Obadiah killed his mother because she was willing to leave him to die for her own gain. He also felt genuinely grateful to Tony for all of the times Tony saved his life despite everything Obadiah had done to Tony and his father.
In Greg Pak's Planet Hulk, Hulk beats the tar out of the Red Emperor, but the baddie's actual demise comes at the hands of the rampaging Wildebots, after the Emperor habitually failed to do anything to mitigate the threat they posed to his citizens. The animated film adaptation of the story features a different, but equally ironic, end for the villain. The Wildebots later rebuilt him and made him realize the scope of his crimes. He is now a cyborg shell of his former self trying to redeem himself while facing scorn and disbelief from his past victims — including his own daughter.
Near the end of the Kree/Skrull War story arc in the Avengers comics, it turns out that the government agent who's been preaching hate against aliens in order to turn public opinion against Mar-Vel (and the Avengers by extension) is a Skrull. Rick Jones (with help from the Supreme Intelligence) remotely shuts down his powers in the middle of a speech, causing him to reveal his true form; the angry mob he was preaching to immediately attacks and beats him to death.
In one story, Batman finds and confronts the man who killed his parents, Joe Chill, but can't find any evidence against him. Taking a risk, he confronts Chill and accuses him of murdering the Waynes, and reveals that he, Bruce Wayne, became Batman because of what happened. He then goes on to tell Chill that he will always be watching, waiting to collar Chill for good. Terrified, Chill runs to some fellow crooks and begs for their help, claiming that Batman is after him because he killed his parents. However, the crooks are furious that because of what Chill did, Batman came to be and ruined their schemes time and time again. In hot-blooded rage they gun Chill down, then realize what a bad idea that was, but before they can get him to spill who Batman is, the 'man himself comes in.
Batman: Still with us, Chill? Chill: Not... for long! Funny... because I started you off as Batman, the boys... plugged me! Yeah... I guess you got me... after all! Ahhhh...(Dies)
In Batman #414, Bats is investigating the mysterious "Dumpster Killer", who leaves women's mutilated corpses in dumpsters (and it becomes personal when one of the people killed is a friend of Bruce Wayne). Several issues later, in #421, Batman discovers the killer is a pair of misogynist douchebags, Karl Branneck & Vito Procaccini, and vows to take them down. In the next issue, Branneck kills Vito because he views him as a liability; later, Batman arrests him and he goes to trial, but is set free because a bloody knife Batman found at his house was found illegally. After making sure Batman isn't around, Branneck then sets out to target another woman... who promptly slits his throat with a straight razor (and is revealed to be the sister of his second victim, who has been personally hounding him so he'd choose to kill her). Fittingly, the name of the last issue is "Just Desserts".
A third example comes from the mini-series The Cult: having been freed from his imprisonment and recovering from his mental and physical trauma, Batman and the Jason Todd Robin storm into Gotham to take back Gotham from Deacon Blackfire, who has taken it over with his army of similarly kidnapped and broken people. Batman finally confronts Blackfire and proceeds to beat him within an inch of his life before stopping; he couldn't arrest him nor, even if he didn't have his code, kill him - they'd just make him a martyr. Instead, he leaves Blackfire, broken and beaten, in front of his followers who literally tear him apart because his broken and pathetic self spat in the face of everything he drilled into their heads.
In the DC Comics miniseries "Final Crisis: Revelations", after Libra kills the Martian Manhunter by means of lighting him on fire to show the assorted villains in his Secret Society that he could make their wishes come true, The Spectre goes after the people who wished it to happen. He turns Dr. Light into a human candle (that is he turns his body into wax and sets his head on fire) and turns Effigy into a melted puddle of a man by boiling him alive. Sadly, it doesn't work for Libra, but The Spectre does kill all the other villains in the room who tried to stop him instead.
Said villains, the Hangmen, are also an example. Spectre hanged them.
In the mini-series Legion of Three Worlds a couple discover Superboy-Prime after he arrives in the future and he vaporizes them in passing. What makes this a Karmic Death? In an earlier storyline, the same couple discovered an alien child, Last of His Kind, in their yard... and vaporized it, burying its remains in their farm.
Aquila: Locusta violates the sanctity of Vesta's temple to revive the dead as unholy abominations. She ends up entombed alive, with the demonic babies she'd revived closing in on her.
In the final issue of Atomic Robo And the Dogs of War, the second half takes a time skip to the 70's when Robo finally finds Otto Skorzeny after looking for him since WWII. He goads Robo, claiming that he had personally killed Nikola Tesla, Robo's creator, and stolen his ideas. Robo takes a gun, aims it at him, and... points it away, and tells Skorzeny that he already knows he's dying of cancer, and instead of giving him a quick soldier's death, he'll leave Skorzeny to die alone and painfully from his cancer.
Long-running newspaper comic Dick Tracy makes karmic deaths of villains one of its defining features. But as of late, the strip has become a surreal series of storylines that are basically long, Rube Goldberg-like marches to see what gruesome end awaits the villain of the story, to the point where Dick and crew will abandon police procedure and common sense (and occasionally, the laws of physics) to facilitate said karmic fate. For example, the storyline where the Big Bad gets torn apart by his own attack dogs after losing his protective whistle; all the while, it never occurs to Dick or his crew to shoot the damn dogs until LONG after the villain is a literal dog's dinner.
Dynamo5: For years Captain Dynamo/William Warner was a habitual womanizer who cheated on his wife, Maddie Warner, even when it compromised his crime-fighting duties. He also was not above using his shape shifting power to impersonate married women's husbands in order to sleep with them. So his death in bed by being poisoned by the woman he was sleeping with can be seen as his cheating and sleeping around finally catching up to him.
In one Star Wars comic, Mako Spince, an old smuggling friend of Han Solo's, sells him and his wife Leia out to bounty hunters hired by Hutts for the death of Jabba. They manage to escape, and later on in the series the same man sells them out to Imperial forces. Han retaliates by flying right next to Spince's flight control tower, causing it to become caught in the Star Destroyer's tractor beam. The Imperials, rather than cut the power, increase it, and the traffic control tower, with Spince cursing Han, is torn up and impales the SD, killing all of them.
The Governor from The Walking Dead suffers one of these at the conclusion of the "Made to Suffer" arc. After the remainder of his troops have finally broken into the good guys' sanctuary, scattering them to the wind and killing over half of them, one of his soldiers, at his urging, shoots a fleeing survivor... the main characters' wife and infant daughter. Upon discovering the Governor made her kill a baby, she empties her shotgun into the back of his head. The entire squad of soldiers get Karmic Deaths as well, as they're implied to be overwhelmed by zombies a moment later.
Scooby Apocalypse: Velma's brother Rufus is one of the Four - the people responsible for the nanite plague that turns most of the world's population into monsters. He's totally unrepentant about this, and has even convinced himself that the monsters are worshiping him. As such, he lets them into his tower in order to kill Mystery Inc... only for the monsters to completely ignore the gang and grab Rufus, dragging him out of the tower to be burned alive in a giant effigy of himself.
Spawn has Malebolgia, the main villain of the original 100 issues, finally killed when Spawn slices off Malebolgia's head with a holy weapon taken from an angel that Malebolgia killed barely five seconds prior. After Malebolgia spends the entire arc manipulating, tormenting and trying to enslave Spawn through the crooked deal that started the series, it comes off as completely karmic.