How about Light from the classic story "Ghost Light"? Wants to kill everyone and everything, because we keep changing and that's just confusing.
Weeping Angels? Angelic statues which kill you by teleporting you into the past and feeding off of potential abstract energy.
The Time Lords, Depending on the Writer, and the Doctor even more so. Half the time he's being portrayed as Jesus, half the time he's committing highly dubious acts without actually realizing he's doing something wrong. His perceived morality varies from Doctor to Doctor, but should never be deduced from his manner and face.
In Midnight, the light is literally killer. Life is thought to be impossible on Midnight's surface, which raises the question: Who's that knocking?
This is touched on in Carnivāle, as there seems to be no moral dimension for being the Creature of Light or the Creature of Darkness; the latter just seems to spread calamity around himself whether he wants to or not. The current Creature of Light is a decent, albeit extremely reluctant guy, but his predecessor is ruthless, manipulative and cruel. Interestingly, he's not beautiful in the slightest, despite being associated with Light, and prefers to hide behind a curtain or make himself invisible to keep the shroud of mystery around himself.
Samson also mentions it in his pilot monologue: "...A false sun explodes over Trinity..." This is a reference to the Trinity Test of the first atomic bomb (a perfect Real Life example of this trope).
Babylon 5 has Vorlons, who look like angels and seem to be helping the younger species fight off the evil Shadows. However, it turns out that the conflict is not between good and evil, but between stasis and chaos. Neither extreme is beneficial for the younger species, who are exploited as pawns in a deadly game. Ultimately, the younger species band together to kick both the Shadows and the Vorlons out of the galaxy.
The Red Woman in Game of Thrones preaches a following to The Lord of Light, which for some reason demands sacrifices in the form of burning people alive and rather fundamentally insists on a "one true god" while other Westerosians speak of old and new gods and seem fine with people believing in one or the other.
The antagonist in the Farscape episode "Crackers Don't Matter" wanted Moya to generate as much light as she could, and used hypnotic patterns in the light generated within the ship to set the crew against each other. We don't find out what he wants the light for, only that it has something to do with what his species wants and they seem to be a threat to everyone else (even though, after he's killed, we never see anything like it again).
Merlyn's turn as an avenging angel who still dresses in holy white on American Gothic, in the episodes "Inhumanitas" (a dead giveaway by its name) and "The Plague Sower." The fact the latter is a callback to the The Bible and a reminder that this trope is Older Than They Think doesn't change the fact she's left good behind—it takes Caleb revealing to her how she's become Not So Different before she returns to her usual self.
In one of the Season 6 'Immortal of the day' episodes of Highlander: The Series, the villain is the head of a global charity organization, always seeking donations and preaching hope, charity and mercy. When he ambushes the main character in a carport with two henchmen, this bit of dialog happens:
An episode of Star Trek: The Next Generation had Data and the Enterprise computer infected by a program from an archeological artifact, forcing the ship's crew to play out an ancient ritual of a sun and moon exchanging places in the sky—from day to night, in this case. The ritual depicted the soothing, gentle moon convincing the harsh, burning sun to leave the world in peace for a time, to keep the sun from destroying everything.
Another episode, "Justice", has the enterprise discover a utopian planet of healthy happy people who wear white and enjoy sexual intercourse. Everything seems peaceful and perfect until Wesley gets sentenced to DEATH for falling through a green-house window.
Supernatural makes a point out of doing this with all the angelic characters featuring from season 4 onwards:
Early in the series, an "angel" actually the ghost of a priest made people commit murders for the sake of considering them evil. He manifested himself surrounded by light, something unusual for a ghost.
Contrast the Winchester's angelic ally Castiel with Uriel in "It's the Great Pumpkin, Sam Winchester!" Uriel is fully willing to destroy the Adventure Towns that Sam and Dean have stumbled upon to stop the demonic baddie of the week from being raised (and a seal to the Big Bad's prison destroyed in the process), and he openly refers to humanity as "mud monkeys." Notably however Castiel would have helped destroy the town if ordered to, it's just he would have felt bad about it.
There's also Zachariah and his lackeys. At first, they just seem like smug, superior Jerkasses. And they are. They also want to set off the apocalypse. Or as Zachariah called it, "A cosmic enema." Zachariah also has another wonderful moment later: When Michael needs consent to take over Dean's body, Zachariah gets persuasive. Not content with giving Dean stage 4 stomach cancer and ensuring Bobby will never walk again, he cheerily announces "Okay, then let's get really creative. Let's see how Sam does without his lungs."
Zachariah does mention, however, that heaven's plan was being kept secret from the "grunt" angels, implying many of them wouldn't have gone along with it if they had known.
In the season 4 finale, the ending makes a large change as it fades to white instead of black. Guess who's shining radiance is approaching? Lucifer. Also, in the flashforward episode, Lucifer in Sam's body wears a perfect white suit and shoes.
Remember the Trickster? Liked teaching people lessons in very cruel ways, stuck Sam in a time loop and killed Dean every single day? He's the Archangel Gabriel. And he's on their side.
Crowley reminded us early on that Lucifer is an angel. However, Lucifer only created the demons (from human souls) to prove to God just how debased humans really are. Lucifer himself feels nothing but contempt for the demons.
Naomi is attractive, has a somewhat cold, but brightly-lit office and is very much a prim angel. She is not really any nicer than Zachariah, just not as obvious about enjoying cruelty.
The final seasons of Stargate SG-1 saw villains in the Ori, ascended beings posing as gods (fire gods, really, but they do a lot of light stuff) and trying to convert the Milky Way galaxy to their religion (Origin) so they can use their collective faith to power-up and take out the Ancients. Their religion seems pretty Christianity-inspired, including having their own holy book (The Book of Origin) and inducing immaculate conception in a major character.
However, the Ori fire motif was eventually contrasted with the soft-white light of the Ancients, who also inserted the concept of "fire is evil" into almost every human culture.
It wasn't played up a lot in It's Always Sunny in Philadelphia, and it was a role in Charlie's play, not his actual persona, but this kicks in when you realize Dennis of all people was cast as Dayman in Charlie's play/demonstration of his memories of being implicitly molested. Dayman himself isn't evil being "a master of karate and friendship for everyone" (that would be Nightman), but Dennis is the person playing him.
In Battlestar Galactica (Reimagined), the visions involving the Final Five are decidedly ominous even though the Five are clad in white robes and surrounded by white light. In addition, D'Anna is instantly struck down after trying to approach one of them. Yet the actual Five straddle more along the lines of Good Is Not Nice.
The Light Fae in Lost Girl are only good by comparison to the Dark in that they have some rules about feeding off humans.
That episode of Nikita where Alex was interrogated using a mind altering drug and she sees her evil self "Alexandra", representing what her life would have been if she had never met Nikita. Alex wore black jogging pants and sweat shirt while "Alexandra" wore this pure white sable fur coat.
The Tarrs in Defiance. Like all Castithans, they have white skin and hair, as well as golden eyes, dress all in white or light grey, and have an entirely white house. However, they're basically the town's equivalent to the Corleones. The Castithans themselves also count; when they led the Votan they kept the other races in subservient positions and attempted genocide on the Irathiants, herding them into caves and then gassing them.
Kamen Rider Wizard has The White Wizard. At first, he actually seems like a good guy and a person Haruto looks up to, but later down the track, once he shows his face to Haruto, he shows this trope, or at least show that Good Is Not Nice by injuring one of his allies into a deep coma and kidnapping a kid who refused to become a Wizard. It is eventually revealed that he is also Wiseman, having manipulated both sides for his own goals.
The Big Bad in 'Neverwhere'' is the angel Islington, who (at least in the original TV miniseries) wears a white robe and lives in a chamber filled with lighted candles.
The Blackadder II episode "Beer" introduces Edmund's relatives the Whiteadders, whose piety and holiness stands in stark contrast to arch-cynic Edmund. However, it turns out that they're even more evil. Or at least she is; he's under a vow of silence and goes along with whatever she says, presumably for fear that she'll turn on him and burn him as a heretic. Until they both get rat-arsed on the eponymous drink.