Also, Pip. No appearances for eight years and then he shows up for ten seconds just to get stepped on by Barbara Streisand.
Happens to a lot of one-episode characters, especially during the first two seasons. For example, Tom and Mary in the episode "Cow Days." They won an all-expense paid trip to South Park and were thrown in jail after arriving, where they were completely neglected and eventually died of starvation.
There was also a minor classmate known as Lizzy, who seemed to be a Distaff Counterpart of Kenny when they gave her a speaking role in season 4 (wearing a pink parka and having lewd language, though she was not muffled). She winds up being carried off by a bear at the end of "Cartman's Silly Hate Crime" after her and the other girls have a sled accident. While the official site FAQ doesn't give a clear answer, they do suggest that she died. Still didn't stop the animators from utilizing her character model in later episodes (though it appears they phased her out completely after a while).
The episode "Spooky Fish" opens with a space ship landing in South Park and a creepy alien coming out to presumably reek havoc on the town. The alien is immediately run over by the school bus, and nobody even notices.
Chef. Though it's more like he was dropped off the bridge.
And lest we forget, one of the early Running Gags of the series was repeatedly dropping bridges on Kenny (only for him to be perfectly fine once the next episode started)
And in-universe, Cartman writes a Christmas short story and does this to the story-version of Kyle, who survives being impregnated with the Anti-Christ and then having an abortion (It Makes Sense in Context) only to be killed off two weeks after the denouement just to troll the real Kyle.
Avatar: The Last Airbender : Jet. Lampshaded in "The Ember Island Players" episode, wherein the main heroes' journey is re-enacted in a play, including the rather ambiguously depicted death of Jet.
Zuko: Did Jet just...die?
Sokka: You know, it was really unclear.
Winx Club: Not a death, but still anti-climactic. One S3 episode sees the Winx breaking a Brainwash spell on Sky to take him back from his original fiancée Diaspro (who had done this for revenge). Several episodes pass without either of them, before Sky finally shows up at the end of one episode to mention that Diaspro was banished. This was anti-climactic because the last shot of Diaspro of season 3 looked more like she was thinking of getting back at the Winx for that. (And she actually did say, "This isn't over! Sky will be mine!" in the original.)
She's back in Season 5, first helping Skye regain his memories, then as an advisor to him/his parents. She seems pretty deliberately unhelpful, and tells Bloom to her face that she's trying to steal Skye from her. Again.
Mirta also went this route. She was turned into a pumpkin halfway through the first season and, once she was restored, only seemed to show up in the background unless the Winx were going to Cloud Tower; considering that she saved the Winx's lives a few times, this seems particularly harsh. And apparently, just to show the fans that she's never going to be a major character, she was shown to have been held back a grade at the beginning of Season 5, being the only character from the Winx's time as students (the first three seasons) who is still attending Alfea when they return after spending a year after graduating on Earth.
In TransformersThe Movie, Optimus Prime, the great leader of the Autobots, dies from wounds suffered during a duel with Megatron, most notably being shot at point blank range by an energy pistol. They later brought him back as a zombie, a ghost, a lifeless body driven by a Japanese trucker, and it's now customary for Optimus to die over and over again, and bring him back through some mystical means, making this more of a Put on a Bus in recent memory.
At least Prime got a decent death scene. In the 2007 movie, Jazz is ripped in two by Megatron and summarily ignored until after the battle, when there's literally less than half a minute of Ratchet carrying over the two pieces of his corpse and Prime being sad before going on to soliloquize about the new friends they've made on Earth. A repaint of his toy model features the blurb that he was brought back to life by the remaining fragment of the Allspark, but Bay says he will not be appearing in the next movie.
Well, his was still better that the deaths of Ratchet, Brawn, Prowl, and Ironhide in the animated movie who were mowed down by Megatron and Starscream in less than ten seconds. And there are plenty more deaths that aren't even shown.
Most of the deaths in the movie are pretty ridiculous, honestly. Not least because they're killed by wounds they'd normally survive (at least one character dies from being shot in the shoulder!)
At least Ironhide gets plenty of lines, and gives us a chance to get to know him if we're not already familiar with him before he dies. Ratchet and Prowl, both featured characters in the cartoons, don't get any lines before they're brutally dispatched. And then there's Wheeljack, an important supporting character on the show (the Autobots' 'go-to' guy for inventions), who dies off-screen and is only shown in the movie as a lifeless burnt wreck.
Ultra Magnus in Headmasters, at the hands of Sixshot. Also, near the beginning of the season/series, Optimus sacrifices himself to stabilize Vector Sigma.
And then there's Galvatron, who survives being at the center of the destruction of Cybertron, only to apparently be Killed Off for Real by having an iceberg dropped on him (there wouldn't happen to be a bridge frozen somewhere inside that iceberg, would there?).
In defense of Starscream's constant survival, it was stated in the Beast Wars show that Starscream's spark was mutated in such a way as to be indestructible. However, whether or not this matters in regards to his body is up for debate. plus it doesn't negate any other death defying character survivals.
Not to mention Blurr's sudden death at the hands, erm, walls, of Longarm/Shockwave
And Ultra Magnus being beaten into a coma. Since the series is over and he didn't get better, this may be considered a bridge drop or Bus Crash.
G.I. Joe did this to Serpentor in the "Operation Dragonfire" mini-series that launched the DiC-produced seasons after the original Sunbow-produced series was canceled. After Cobra Commander was turned into a snake during the events of G.I. Joe: The Movie, he returned to his human form to get his revenge. Serpentor, the one who turned him into a snake, is easily captured and turned into an iguana. Gnawgahyde, one of the Dreadnoks, says "I think I'll put him on the barbie". We never see Serpentor again after this...
In the finale of Justice League Unlimited, the combination of Killer Frost and Darkseid's return drops a bridge on roughly two-thirds of the Legion of Doom, including established and well-characterized (if secondary) villains such as the Shade, Parasite, Copperhead, and Weather Wizard.
Ben 10: Alien Force apparently did this to the Galactic Enforcers, a group of Justice League spoof from the original show, in Revenge of Vilgax, with the three of them being easily defeated and possibly killed (or, for Ultimos, at least stripped of his powers) by Vilgax at the beginning. We never heard of them again.
Also, Pierce, a secondary but well-characterized character introduced in Alien Force, was unceremoniously disposed of by the Forever Knights in Ultimate Alien to show they had finally gone out of their Badass Decay. His death is never mentioned again, and we don't even get to see the reaction from his sister.
Happens In-Universe on the Rocko's Modern Life episode "I Have No Son": A Fatheads episode opens with two pigs having a picnic near a lake. One comments on the absurdity of pigs speaking English, only for the Fatheads' spaceship to abruptly drop on both pigs.
Lampshaded in the Futurama episode Calculon 2.0. Calculon, whose acting style is akin to William Shatner's, is dramatically brought back to life for a final performance and then crushed first by a falling studio lamp and a catwalk that looks suspiciously like the bridge that killed Kirk in Star Trek: Generations.
A Cartoon Network promo for the show Tazmania did this. Taz squares off against a koala in a fictional game show called "Pick Your Marsupial." Just as the host is about to describe what Taz eats, he abruptly devours the unsuspecting Koala and is declared the winner by default.