24: Established its Anyone Can Die cred early in the first season by killing off Kim Bauer's innocent friend Janet York early in the first season, then in a big way by killing off Teri Bauer in the first season finale. By the end of season six, only Jack and Tony are still alive out of the Season 1 agents.
Angel: The show that killed one of three main characters in the ninth episode and then three of five main characters in the fifth season: Fred, Cordelia, and Wesley. Not to mention said last episode ended with four main characters, one of whom (Charles Gunn) was quickly bleeding to death, charging into battle against a huge army of darkness, with the very strong impression that no one would survive. And that's not even getting into After The Fall (which had almost everyone before the Reset Button). Let's just put it this way: the life expectancy of a character in any show created by Joss Whedon is rather lower than the average.
Babylon 5: Tended to do this too — one watched each episode wondering who was going to "get it" this year, although in this case it was all part of the Myth Arc and less of a shock effect. Of note, some characters like Jeffrey Sinclair were unexpectedly written off (cases of Real Life Writes the Plot) without being killed, and would sometimes return.
Lt. Keffer was created and introduced specifically for the purpose of being later killed off in order to let the main characters know about the existence of the Big Bad, after being pressured into including the character by Executive Meddling from Warner Bros., at least according to the DVD commentaries. The actor playing the part wasn't even told his character was dead until later.
And the first season episode "Believers" hammered it home: an alien child will die without surgery, but according to his parents' religious beliefs, cutting his chest cavity will cause his soul to disappear and leave him a soulless abomination. Dr. Franklin goes against their wishes and performs the operation. The parents then kill the 'soulless' child.
Not only do they kill off main characters, they do it with style. Bester, in one episode, implies not only that Talia Winters is dead, but that she was actually dissected for research, though it's just as likely he was trying to get a rise out of the others. Furthermore, Marcus Cole dies to save Ivanova without telling how he feels about her. Then there's G'Kar and Londo killing each other in a flash-forward.
The character of Carolyn Sykes/Catherine Sakai/Anna Sheridan survives numerous rewrites, re-assignments of role, and even posession by the Machine, to be exploded by John Sheridan. With two nuclear weapons. And Mr. Morden, a few yards further from ground zero, survives.
Band of Brothers: This is pretty much a documentary with actors instead of "plain old television," but it's a case where reality beats the holy snot out of this one. Granted, it's war, and in war anyone can (and does) die, but it's still rather jarring to spend hours getting to know characters only to have them disintegrated by a direct hit from an artillery shell, have a leg blown entirely off while trying to help a squad mate, or finally find the Luger they've spent the entire series hoping to find, only to have it go off shortly after finally getting it and having the bullet hit the femoral artery and have the man bleed to death while being held by his buddies.
Battlestar Galactica: The new series was notorious for this. Although some characters could come back if they were Cylons, most other characters had permanent deaths and it happened frequently. Even a Redshirt death tended to matter, since background characters were recurring.
Being Human has a very high body count. By the end of the fourth series, all four of the original main characters have been killed off, leaving the fifth series to focus on a whole new vampire-werewolf-ghost trio.
Blackadder: Each series was set in a different era. The final episodes of each era were ones in which indeed, Anyone Can Die.
Boardwalk Empire: At least one significant character dies in each of the final three episodes of the second season: first Angela Darmody, then The Commodore, and finally (and most shockingly) Jimmy Darmody. (A somewhat less important character, Boss Neary, also dies in the season finale.) Continues into season 3 with the deaths of Manny Horwitz, Billie Kent, Owen Slater and Gyp Rosetti and season 4 with the deaths of Eddie Kessler and Richard Harrow, arguably the show's most popular character.
Breaking Bad: At first the show started out by killing only a few Mauve Shirts or criminals who clearly had it coming, but as the series progressed, more and more supporting characters (like Combo and Jane) started to die to remind the audience just how dangerous drug dealing, meth cooking, etc. really is. By Season 5, the situation has become so out of control that all of the main characters lost their Plot Armor, and a few of them wound up getting killed.
Xander's friend Jesse dies in the very second episode of the show. Whedon had wanted him to be in the opening credits to really drive the point home but this was prevented by financial considerations.
The episode Tara appears in the opening credits for the first time is also the episode she dies in, after being on the show for two seasons.
Buffy herself died twice, in the season 1 and season 5 finales. Her second death was intended to be permanent; she was resurrected when the show was renewed and moved to a new channel.
Whedon even suggested, on two separate occasions, to kill off Xander: once in the Season Five finale, and later at the hands of Caleb near the end of Season Seven in the episode "Dirty Girls" (which was reduced to him losing his eye). The latter plan was really only abandoned when they realised there wouldn't be sufficient mourning time for the character in the final four episodes.
Anya died in the series finale, being nearly bisected.
It was originally intended for Dawn to sacrifice her life—and disappear forever—in the last moments of "The Gift" before they decided that Buffy dying for her sister would be a more meaningful way to go.
Jenny Calendar is killed by Angelus in season 2.
Joyce Summers dies from a brain aneurysm, one of the few natural deaths in the series.
Giles dies by the hands of a possessed Angel near the end of season 8.
A recurring character since the unaired pilot, Jonathan is killed by Andrew in season 7.
Caprica: Probably the ultimate example of this trope comes in the prequel series to the new Battlestar Galactica. Galactica, of course, starred Admiral Bill Adama, son of Joseph Adama, so when Caprica introduced us to Joseph Adama and his young son William, certain assumptions of Contractual Immortality were made. Then the penultimate episode killed off William. Joseph names his next son after the dead one.
Choujuu Sentai Liveman: If you're a non-human, one shot character, you WILL die, no matter how much character development you get. Then there are the villains, who the Liveman are actively trying to save. Only Goh/Dr. Obular lives. The rest all die. And a majority of them are even a case of Redemption Equals Death.
Chuck: The third season seems to want to establish this early on: at the very beginning of the season the show breaks one of it's unwritten rules by having an enemy agent kill a recurring Buy More employee, Emmit.
You can also add Bryce Larkin (who died at the third season's end) and possibly Stephen Bartowski (who got killed in the season three finale). On the villains' side, Smug Snake CIA representative Decker bit the bullet half-way through the fifth season.
Cranford: Truly anyone can die. Prominent characters, secondary characters, young people, old people, children, pet animals. The causes of death are varied, too: long illness, sudden stroke, infection, accident, childbirth... you name it, you got it. No one is safe on this show, ever.
CrossingLines In Pilot Part 2 Sienna of of the cops is killed, just after the kidnapped Anne-Marie is saved because she disrupts the serial killer's ritual
Damages: This is combined with Anybody Can Go To Jail thanks to Revolving Door Casting as the result of most of its supporting cast being made up of film actors. The first season alone has two Sacrificial Lions and by the end of the third season only two of the show's original cast members aren't dead or in prison. This is to say nothing of the high mortality rate of recurring characters. With the exception of Patty's son and ex husband it would seem that as soon as you sign a deal to guest star on the show chances are you'll be looking for work again once shooting is over.
Dollhouse: By the end, Boyd (who is actually the Big Bad), Topher (Heroic Sacrifice), Paul (shot moments before reaching safety in the finale, although his memories get uploaded to Echo), Mellies (shoots herself when programmed to kill Paul), and Bennett (shot in the head by Saunders) are dead.
Earth: Final Conflict: This show was infamous for taking this to ridiculous extremes. Only one character (a villain) is featured in all five seasons and most characters die or otherwise in some way get practically removed from the main cast within one and a half season of introduction.
In fact, one episode was completely devoted to an episode-long demise of a minor character which only featured in four episodes. Though the character was instrumental for the plot as she was one of the three parents of a character which lasted three whole seasons.
ER: The very very very long running drama has featured deaths of multiple main characters. However, as the cast is forever large and rearrangable, with plots being recycled all over, this is perhaps not so difficult as for a show with a smaller established cast.
Falling Skies: Downplayed. Although the main cast is (relatively) safe, an incredible amount of minor, supporting, and major cast members have bought it. The show most recently killed off Karen in an anti-climatic fashion, who had been built up across three seasons as the Big Bad and was gunned down without warning by Tom and Maggie in the Season 3 finale. It will most likely not get better in Season 4.
Fame: The series version had an episode during its final season (airing in early 1987). That episode ("Go Softly Into Morning") saw Nicole Chapman and Danny Amatullo miss a rehearsal; with it being revealed that the two (along with another drunk student) were involved in an accident, resulting in Nicole being killed and Danny badly injured.
Game of Thrones: The Season 2 Trailer pretty much invokes this in-universe with Arya saying "Anyone can be killed".
The series follows the books it's based on very closely, and books tend to follow this trope more often than live-action series. This is shown prominently at the end of the first season, when the main character, the one given top billing (as well as being probably the most famous actor cast in the series,) got his head lopped off. Network Executives were apparently hesitant about killing off the main character of the series one season in, and understandably so. Then they saw the ratings. They were cool with it after that.
And if you still weren't convinced, there's episode nine of season three. Robb's wife dying? Kinda sad. Catelyn dying? Totally awful, but at least somewhat inferrable from Ned's death. But Robb dying?!
All three dying in the same episode, within the span of a few minutes of each other, in the same scene - priceless
They even killed the dog!
Greys Anatomy: Both Izzie and George die in the season 5 finale. Who knows whether they'll return in season 6 due to contractual immortality.
Unless certain people changed their minds on the issue, Izzie recovers but George stays dead.
Not to mention Denny Duquette (who may or may not be a hallucination/angel)!
As of the Season 8 finale, Lexie Grey, in a plane crash
As of the Season 9 premiere, Mark Sloan due to injuries from the plane crash. Adele Webber also dies.
Harper's Island: Kills off at least 1 character every episode, with the phrase 'One by One' as it's tagline. Out of the 25 presented characters, only 4 live through the series.
The ultimate example is Da Chief (who is also the father of one of the main characters).
Heroes: The original concept behind the show was that, not only could anyone die, but by the end of the first season it was expected that a majority of the cast would die with the survivors Put on a Bus to make way for a new season 2 cast (the actors were told as much when they originally signed on). This changed due to the popularity of the original cast with fans, and many of the characters who appeared to die in the Season 1 finale would turn out to be Not Quite Dead. Nonetheless, they did manage to kill off two of the main characters, as well as most of the recurring supporting cast.
The deaths of Isaac, Alejandro, Peter (temporarily) and Kaito were certainly unexpected. Not to mention Niki.
Newer characters get killed off while the older characters get Joker Immunity. We're looking at you, Sylar.
Volume Four: Nathan Petrelli.
Kamen Rider 555: As the shiny suits can change hands in this series, even being one of the three main Riders will not protect you.
Kamen Rider Kabuto isn't as dark as 555 but the final episodes take a turn for the brutal. Say adios to three Riders.
Law & Order: Det. Max Greevey in the season two premiere, ADA Claire Kincaid in the season six finale, and ADA Alexandra Borgia in the season sixteen finale.
Law & Order: Criminal Intent: Capt. Danny Ross is murdered in the season premiere while working undercover with the feds against an arms dealer.
LOST: This show is notable for its death rate. Of the 14 original main characters, 9 are dead by the end of the show, leaving only 5 still living, and of the 35 characters ever given main cast billing, 21 end the show dead, leaving just 14 alive.
Furthermore, of the 73 survivors of the plane crash, only a measly 12 are known to be alive at the end, and at least 32 of the other 61 are definitely dead. So much for "survivors".
Lampshaded / foreshadowed in an episode when Daniel Faraday says exactly "Any one of us can die." At the end of the episode, he dies.
Word Of God is that Jack was supposed to be killed by the Smoke Monster in the pilot episode to show that even the most important characters were not safe. Executive Meddling prevented this, however, as ABC believed viewers were more likely to feel betrayed. They ended up killing the pilot of the plane in his place.
Merlin: The 1998 series has numerous deaths, both of heroic and villainous characters.
Merlin: The 2008 series had a notorious reputation for Status Quo Is God. Then Season 4 rolled around, and they kill Lancelot in the second episode with absolutely no warning. They avoided Dropped a Bridge on Him, but it was still shocking.. Well, at least the next episode will be a Breather Episode... then Uther dies?!
Lancelot does come back later in the season. For about ten seconds after Merlin releases him from the spell that made him a Soulless Shell after he Came Back Wrong. Word Of God confirms he's gone for good now.
Misfits: For a show whose series 1 finale spoiler was that a main character could not, in fact, die, by series 4 finale none of the original cast is still around, most of them having died. To say nothing of the probation workers.
NCIS: Especially if you happen to be female. Title credits offer no protection.
Michael Weatherly joked that NCIS stood for "No Castmember Is Safe"
Oz: This show is notorious for leveraging this psychological trope and it was a big part of the premise of Tour of Duty.
Oz is so committed to use of this trope that its official website includes an interactive death map showing all the characters, which ones were still alive at the last show, and where the rest of them died. Borders on Kill 'em All.
The Pacific, a successor series to Band of Brothers has a high death rate, and kills off one of the three protagonists.
Person of Interest: Downplayed. So far only one main character has been killed off the show. Everyone else who died was either a recurring or minor character.
Primeval: The show is sometimes turning to Anyone Will Die, as at least one major character died each series, with Nick Cutter himself dying MID-SERIES in Series 3.
As of the end of Season 3 there are only three main characters left from S1. They must be nervously checking their contract for S4...
Series three is especially bad. In that one series alone, Nick is shot by Helen, causing Jenny to leave (even though she somes back for an episode in series 4), Cristine Johnson is killed by a future predator, Helen falls off a cliff, and Connor, Abby and Danny all get stuck in different time periods with almost no chance of surviving or ever getting back home. Even though the last three get back, that leaves only Lester back at the ARC from the very beginning.
In series 4 we find out that Sarah died.
Prison Break: Beginning with its second season, the show kicked its extreme Anyone Can Die atmosphere into overdrive, bordering on Kill 'em All with its penchant for killing off main characters with the zeal of a slasher film. There's at least a 2:1 ratio for make up kills and subverted deaths, and in one hell of an example of Your Princess Is in Another Castle, the series finale delivers in a big way with the most shocking death of all.
Rescue Me: In the first five season finales someone of importance has gone to meet their Maker in the permanent way.
Robin Hood: The BBC's series killed off MAID MARIAN. She was followed by Allan-a-Dale, Guy of Gisborne, the Sheriffs of Nottingham (both of them) and finally Robin Hood himself.
The Sarah Connor Chronicles: First off, minor characters, like Andy Goode, Charley Dixon's wife, Doctor Sherman, or Allison Young. Then, Riley is killed. Then, Jesse. Then, Charley himself. Then,Derek frakkin' Reese!.
Scrubs: Discussed by JD, who says so many people die that he views Death as just another co-worker (an Imagine Spot plays this out literally). One episode has him say that with a few exceptions (ER, maternity ward, etc.), a third of the patients who come to the hospital will die. JD, Turk, and Elliot each have a patient, and it's implied that one of them will die; however, all three die, with JD saying that sometimes the odds are worse than one in three.
The only main character to die is Laverne, which is shocking because it comes out of nowhere. Ben also dies.
The Secret Circle: Has this trope, as you'd expect from the team behind The Vampire Diaries. Significantly speaking, it starts with Nick and continues on through to Jane, much to the Circle's grief.
Six Feet Under: The father of the family was killed in the first scene of the first episode, though his "ghost" appears throughout the series conversing with the characters, manifesting their subconscious thoughts. Multiple main characters die throughout the course of the series, which itself deals constantly with death, using it as a magnifying glass for life. The most shocking example is the death of Nate Fisher, the lead character, a few episodes before the end of the series. He dies of a brain hemorrhage, and is given a private burial by the Fisher family. The series finale includes depictions of the deaths of every other main character.
Skins: They kill one of the main characters every 2 seasons. Usually, it happens at the end of the second season of each generation, like with Chris or Freddie. Season 6 killed one of the main characters the second episode. This is not counting other characters (parents, friends, enemies, strangers) that died or might have died, for example Sid's father Mark. Kind of a high mortality rate for a series that only involves regular, healthy, teenagers, with no real violence, no super powers, no mystical creatures, etc...
Sons Of Anarchy: Not even being in the credits will protect you. Ask Half Sack. Although, at least he got to the end of Season 2, which is more than Piney and Opie got. Particularly jarring in the latter's case, since he was killed only three episodes into Season 5!
Season 6 really upped the body count. By the season finale, two main characters who have been with the show since the series premiere and no less than seven recurring characters are dead, one of whom was portrayed by the creator of the show! No wonder fans are starting to think that the next season will end in Kill 'em All.
The Sopranos: Anyone Can Die pretty much became the hook of the show. No one was safe, be it the lowest goon or Tony himself. Due to the fact that they were never informed well in advance, many of the actors explicitly expressed suspense and fear for their careers should the writers suddenly choose the sword to fall on their head. (Though in the case of Livia, it was the actress that died first.)
Most of the most notorious deaths of major characters such as Salvatore "Big Pussy" Bonpensiero, Vito Spatafore, Adriana La Cerva and Bobby "Bacala" Baccalieri came, predictably, as a result of mob hits. However, arguably the most shocking death occurred in Season 6 when Christopher Moltisanti is mortally wounded when the car he is riding in with Tony flips over (his death arguably hastened by Tony's mercy killing of him.)
Spartacus:Vengeance was even worse, the finale killed off no fewer than six major characters
Pretty much anything in this show is a Foregone Conclusion since it's based on historical events. Since the Roman Empire continued for a while, it's not hard to figure out who wins the war.
War of the Damned keeps up the grand tradition. By the end of the finale, the only major protagonists left standing are Agron and Nasir.
Agron also has the dubious honour of being the only recurring character from the first two seasons to survive the show, and he only gets introduced half a season into the story. This means the show managed to kill off all characters that it started with and who had more than a line or two of dialogue, as well as everyone from the prequel season.
While not everybody dies, characters are far from entirely safe in the show. Major characters have been killed off with no warning, including all three main characters over the course of a single series. As of the end of season 6, only two season 1 characters remain employed at Thames House.
The short-lived Spin-Off, Spooks Code Nine, naturally had to play with this, killing off the team leader at the end of the first episode. Of course, this being Spooks, everybody was pretty much expecting it.
Series 7 in general is where they took this to the next level - besides the above two, Adam (the only field agent/section chief to break the 40 episode mark) was killed off in the premiere. Series eight also killed off long runners Jo and Ros, and the last seven episodes of the show (starting at the S9 finale) saw the deaths of Lucas, Tariq and Ruth.
Stargate Atlantis: According to Word Of God, this show was purposely designed to be this way. Colonel Sumner is a Dead Star Walking in the first episode and they make a point of killing important recurring characters throughout the series (Grodin and Heightmeyer come to mind.) They finally ramped it up at the end of season 3 by killing Dr. Beckett. They then went even further by killing Dr. Weir a few episodes later, but she was Not Quite Dead. Technically neither was Beckett.
Stargate SG-1: Double Subverted in seventh season. The show convinces us that it's not going to kill off O'Neill. They don't. They kill off Dr. Frasier instead.
The Straits: Harry Montebello starts off more-or-less as the main character. Then he dies. By that time, a fair few secondary characters have already been brutally killed off.
Strike Back has this in spades: none of the Series 1 cast survive, and out of the Project Dawn cast, only Stonebridge, Scott and Richmond have survived up till Shadow Warfare. Everyone else is dead.
Supernatural: Victims of the week are slaughtered with reckless abandon, almost no supporting character introduced survives for even a single season, and NO ONE is immune, though if you're important enough, you may come Back from the Dead. You may even die and come back a lot. Unless you're female.
Of all the characters that have appeared in the series, most have not lasted more than a season or two. Many of the more major characters come back briefly in some form or another, but aside from Sam and Dean, they all return to the land of the dead at some point. The writers also seem to not fear killing main characters for good as was shown in the episode, "Death's Door" when Bobby died.
Following the death of Meg in Goodbye Stranger no character who appeared in season 1 is still alive except for Sam and Dean...and as even they have died repeatedly over the course of the series, the longest surviving characters are now the Ghostfacers.
Survivors: The original 70s version burned through quite a cast-roster in just three seasons' worth of episodes.
Torchwood: Has a Dead Star Walking in its first episode. But that's just the start. Out of the show's five main characters, three of them are dead as of the end of Miracle Day. That's without getting into Jack's immortality. Even by Anyone Can Die standards, a sixty percent mortality rate among the protagonists is staggering.
In fact, Owen dies not once, but twice. Anyone can die... even if they're already dead.
In Torchwood: Miracle Day, Esther Drummond and Oswald Danes died at the end. Dr. Juarez was incinerated just as she seemed to be becoming part of the Torchwood team.
And Esther is shot to force the team not to reverse the immortality granted by the Blessing. They still do it and later lament that the Blessing didn't save Esther. Then another member of the team is shot at the very end... but comes back to life and demands to know what's Jack's blood did to him.
Gwen and the immortal Jack are the only members of the season one team to be alive by the most recent season finale.
Narrowly averted with Rhys, who the writers intended to kill off at the end of Series 1. Eventually, Russell T. Davies realized that his presence was needed to ground the show (as Rhys was a Badass Normal, in contrast to the rest of the cast's skilled, super agents) and to help evolve Gwen's character, so they rewrote the ending to let him live.
True Blood: Certainly exhibits this trope, especially with the fourth season.
Interestingly, Lafayette inverts this from the books. But then pays for it by killing his boyfriend while possessed by the spirit of a mad witch.
Under the Dome: A significant number of the initially introduced characters have already died, with three or more named characters dying off each episode, and few characters not from episode 1 have made it more than a few episodes in before being killed off.
The Unit: They had a Tonight Someone Dies episode right out of nowhere. And no cop-out either. A real main character dies. And it's not even sweeps week.
V: In the weekly series characters were killed without warning, especially characters from the miniseries, to the point in which no character was safe. (Of course, one actor was brought back as his own twin...)
V 2009: Doesn't have much in the way of this, until the second season finale, wherein they really make up for lost time. Three major characters you'd expect to have immunity (they seemed integral to arcs that weren't quite over, so not expendable yet even if their character types don't always make it to the Grand Finale) die sudden and unexpected deaths. Then the show doesn't get renewed, making the episode that killed half the cast and left Earth in its Darkest Hourbecomes the official ending.
The Vampire Diaries: Certainly seems to love this trope, seeing as how they've already killed off thirteen characters. And that's just the first season.
Veronica Mars: Kills off Sheriff Lamb and Dean O'Dell quite unceremoniously.
The Walking Dead: To give you an idea on how bad it's been, out of all the characters introduced in Season 1, including minor, recurring, and main characters, the only ones still alive by the Season 4 premiere are Rick, Carl, Glenn, Daryl, Morgan, and Carol. Everyone else has either died or their whereabouts are unknown.
The Wire: At least one major character dies in every season: Wallace in Season 1, D'Angelo Barksdale and Frank Sobotka in Season 2, Stringer Bell in Season 3, Bodie in Season 4, Proposition Joe and Omar Little in Season 5.
The last was a particularly powerful example of the trope, as Omar was built up as a larger-than-life, unstoppable force of nature throughout the series, only to be shot in the back of the head while buying a pack of cigarettes by a nobody kid...
Not to mention a host of secondary characters that can and will be killed off in droves.
The X-Files: This show was notorious for killing off their beloved characters, given how important characters such as Deep Throat, Mulder's father, Scully's sister or Mr. X died, sometimes in important Myth Arc episodes but at times in relatively unimportant ones. According to Chris Carter, killing off Deep Throat in the first season was meant to establish that everyone, except Mulder and Scully, is expendable. Any agent who would be friends with our Dynamic Duo was in great danger. The authors needed them to show the audience that it was Mulder and Scully against the world. To give them Angst, they would not only kill off their family members, but their friends as well. The score includes Mulder's former partner Jerry Lamana from Violent Crimes, Scully's instructor and ex-boyfriend Jack Willis, Mulder's former boss and mentor Reggie Perdue, Scully's former student Kelly Ryan (though she was a detective, not a special agent), the lovable Lab Rat Agent Pendrell with a serious crush on Scully or Mulder's former partner and ex-lover Diana Fowley (though this one had barely any redeemable qualities). The Lone Gunmen did not make it to the finale either. Notable exceptions were two villains: Alex Krycek and the Cigarette Smoking Man were killed frequently, but it took a long time until they were eventually killed off for good. Also Agent Mulder kept dying throughout the series mostly in season finales as cliffhanger but the audience soon figured out that he would usually get better.