Powers does this really well. Not only does powers get killed left and right, on panel and off, regardless of how established the characters are - that's sort of the premise - but it goes for civilians as well. And the Pope. And the main characters. Once Kutter gets his head ripped off you really start worrying for the leading pair.
This is a large part of the premise of DC Comics' aptly named Suicide Squad, about a black ops group composed of expendable Boxed Crooks and B-list heroes sent on frequently lethal missions.
Standard operating procedure for any comic book summer Crisis Crossover, it's very well-known that as soon as it's Crisis Season, nobody's safe. Although it's also very well-known that anybody who's ever had a solo title will be back.
Peter Milligan and Mike Allred's X-Force/X-Statix took a pretty lethal approach to its cast, killing off all but the two newest members of the titular team in the first issue and continuing to bump off regulars with regularity. It's stated that the team's membership has a very high turnover rate, and that before the series began the roster had been killed and replaced several times. The series partially serves to explore the idea that if superheroes were real, most of them wouldn't live very long.
It's not strictly germane that one of the longer-running characters had, as a super-power, the fact that she was already dead. She still died in the last issue and her follow-up miniseries didn't even really bring her or any of the others back.
This is inverted in one storyline, in which one of the three leads is predicted to die, but they don't know which one. Each deals with their potentially impending death in their own way, and it's a slow, quiet tale for a series in which characters often get blown up with no advance warning. The issue in which the doomed character is revealed bears the simple title, "Someone Dies."
A comedic example: Marvel's Great Lakes Avengers. Er, X-Men. Er, Champions. OK, Initiative. Their big day in the sun, the 4-issue miniseries GLA Misassembled, featured as the gimmick that one member would die each issue. This doesn't count Mr Immortal, of course.
It should be noted, though, that only one member of the original team died and stayed dead during the miniseries, so it was a bit intentionally misleading. And the second issue cheated by introducing a new character who is killed within seconds of joining the team.
The '80s series Strikeforce: Morituri, about an alien invasion being defended against by Super Soldiers whose powers would inevitably kill them — and did. Characters were constantly dying and being replaced by new recruits.
Characters frequently died long before the projected one year lifespan granted by the Morituri Process. For example: Viking died within four issues, perhaps less than four months of time.
This happens often in Judge Dredd. Even the best villains are usually dead by the end of the story they're introduced in. Judge Giant, Dredd's frequent sidekick and one of the most easy-going and humorous characters, was instantly killed after a terrorist casually shot him In the Back during the "Block Mania" storyline. Meanwhile, violent death practically counts as natural causes for the Chief Judges.
Commonplace in The Walking Dead, where usually at least one main character dies per graphic novel. The eighth volume, Made To Suffer, seriously ups the ante by killing off a total of ten characters (only two of whom are villains) ...over half the cast at that point. The only consolation is that most of them died of head wounds, ensuring they don't have to become zombies... and when that's the bright side, you know you've got a Crapsack World. Oh, and also, their sanctuary is destroyed, kicking them back out into the zombie-infested outside world. Sucks to be them. It has not gotten better since the Made To Suffer compilation came out.
Morning Glories. The kids themselves learn this in-universe during their first week of school.
Marvel Comics' Exiles, a book about a group of six characters from alternate universes who are pulled into MORE alternate universes to save them from being "broken" and thus eventually return home, is known for being quite lacking in Comic Book Death, especially for a series with all these alternate universes running around.
Although it doesn't have a lot of deaths Exiles does have a number of key ones. The most notable is likely Sunfire. Sunfire (this version being a Japanese lesbian instead of formal guy in the main verse) is killed by team leader Mimic when he neglects to tell the team that he was infected with the Brood (chest burster aliens), Sunfire was killed off despite the fact that she was one of the more popular characters.
An even sadder version would probably be Thunderbird; a version of John Proudstar who underwent Apocalypse's Four Horsemen Treatment (he became War). Thunderbird becomes permanently brain damaged (until its reversed when the comic starts to suck) and becomes a vegetable after punching through Galactus's armor and setting off a device that causes a full powered Galactus to run away from Earth. To understand how insanely badass this was, in the main Marvel Universe it usually takes divine intervention to stop Galactus, and usually he's half starved with barely a tenth of his full power. The version Thunderbird takes out was scary enough to cause a planet full of skrull to run away
Or how's about the real kicker, Mimic? One of the few remaining original Exiles members and lover to other mainstay Blink, Mimic was possessed by the serial killer Proteus and killed just as it looked like his team members had figured out a way to save him. It was with a whimper that he died, literally, rather than the expected bang, which just made the death even crueler.
This got even more extreme in Transformers Generation 2, in which the writers got more freedom, and suddenly even characters who did have toys on the shelves weren't safe.
The IDW Publishing mini-series Transformers: Last Stand of the Wreckers was built around an Anyone Can Die attitude - the Wreckers being an elite Autobot suicide squad, whose previous incarnations tended to suffer heavy losses. Authors James Roberts and Nick Roche promised that the mini would live up to the tradition - and made good on that promise. As of issue 4, four of the initial eleven Autobots were dead (along with three major Decepticons), and the final issues and prose story brought even more carnage.
The gritty crime series 100 Bullets establishes from early on that any character can die at any point.
Watchmen has a high death rate for major and minor characters. Not only do The Comedian and Rorschach die, but many secondary characters die as a result of Ozymandias' fake alien attack on New York, showing that no characters are safe.
In Wonder Woman, Steve Trevor was killed off, after being a major character for about 30 years, as part of a complete revamp of the character in the early seventies.
This was used extremely sparingly in ElfQuest, starting with One-Eye's complicated and drawn-out death, followed by Kureel in the second long arc. Later examples in the backstory include Crescent (which gets referred to very often), Rillfisher (already alluded to in the main arcs as a trope example), and Thiro (whose death triggered an important moment in the relationship between Leetah and Rayek). Then the Shards war happened, and death suddenly became a whole lot cheaper.
Par for the course in Nikolai Dante, so much so that fans objected to the lack of deaths in the "Prisoner of the Tzar" and "An Army of Thieves and Whores" arcs.
The "heroes be damned" arc more than made up for those two arcs though...
DC and Marvel kill characters all the time. The measure of a good death is how notable the character is and how long it sticks. To that end, the series most faithful to this trope was Crisis on Infinite Earths. It destroys an infinite number of earths, some with important characters, but its most notable for killing Supergirl (which stuck for 18 years) and Flash (Barry Allen stayed dead for 23 years.) After this, you have one earth and most of its old continuity was thrown out (for about 20 years.)
The number of shocking, unexpected deaths in its huge cast was a big part of Negation's appeal.
Narrowly averted in Gold Digger when Cheetah - one of the most beloved core characters - was very nearly written out of the series by way of killing her off... but was spared on the outcome of a coin toss. Yikes.
Neil Gaiman's The Sandman is VERY heavy on character death. Plenty of minor, supporting and even major characters snuff it - sometimes all within a single volume - and that's not counting the times someone happens to receive a Fate Worse than Death. Gods themselves are established as capable of dying, and it's stated that they WILL die when they have no followers left. Even the Endless themselves can be killed, as explained with the original Despair in Endless Nights, and Morpheus (Dream) himself dies at the end of Volume 9, 'The Kindly Ones' - his powers and essence restored within Daniel Hall, the new Dream, as the major plot of Volume 10.
Kirkman's Invincible keeps you guessing about who'll die and who'll return from fatal injury, whether one's talking about villains, heroes, or innocent bystanders. The tone is set early on, when the Invincible world's equivalent of the Justice League is introduced as fleshed-out characters, and then brutally killed off by Omni-Man. Their replacement really, REALLY suffers throughout the series as well, especially against the Lizard League, and against the invasion of evil parallel-universe Invincibles. The series also tends to keep you guessing, since the government has insane medical technology (along with various aliens having even more ridiculous medical technology), and a lot of characters have ways to circumvent death and/or the ability to survive wounds that would be fatal for normal people. The Sorting Algorithm of Deadness is hard to apply, as a result.
Self-parodied with the issue #100 storyline, "The Death of Everyone". The only named character who dies is the villain, though millions of nameless civilians die.
The X-Men story arc known as Age of Apocalypse was especially brutal - starting with Xavier's accidental death before the X-men are founded (prompting a new future, where Magneto founds the team and Apocalypse starts his takeover much sooner), it becomes one of the darkest Alternate Universes ever. Heroes are villains, villains are heroes, and it becomes a veritable bloodbath by the time all is said and done. Of course, said reality ceased to exist once the X-men successfully Set Right What Once Went Wrong, but that doesn't make it any less shocking to have seen all those people - mutant and human alike - dropping dead like mayflies...
And now it's been reestablished and is even grimmer than back in the 90's. Uncanny X-force (Wolverine's death squad) presented us with Age of Apocalypse Wolverine as the new Apocalypse, armed with a bunch of reinterpreted A-listers as his backing band.
It's not uncommon for Sin City stories to end up with dead protagonists despite the narration. Considering the series is in Anachronic Order, readers can always expect to see the characters again even if they have died previously. For instance, Marv died in the very first story of the series and yet he has had many appearances since.
In Ultimate Marvel, there was their mega-crossover Ultimatum in 2008-2009, which basically exists to brutally kill massive numbers of characters for the shock value. The Ultimate X-Men were hit the hardest, with only five members surviving. How much of it is Comic Book Death remains to be seen.
Marvel's answer to Green Lantern: Quasar has died so often that when the mini-series Annihilation was announced in 2006. The first question asked by a fan of the creative team was basically "Does Quasar have any chance of surviving this series??" The answer was, "no."
As note at the top of the page, Marvel and DC run on anyone can die (flagship characters like Spider-Man, Superman, and Batman die all over the place), but the catch is that Death Is Cheap to extremes.
While arguably not as bad as Ultimate can be-the main character has yet to die-the main 616 Spider-Man comics can be still be pretty bad about this. Uncle Ben may have been an example of Death by Origin Story and Gwen bit the dust to give Peter even more to angst about, Kraven The Hunter, The Green Goblin, Jean De Wolfe, Captain Stacy, Mary Jane, Aunt May, Madame Webb, Mattie Franklin, Nick from the Bugle, The Hobbgoblin, Ned Leeds, Ben Reily, Harry Osborn etc. didn't know what hit them. Granted a lot of those guys failed to stay dead, but they managed a lot longer than most. (The exceptions to the long death thing being MJ-whom even the writers thought killing off was a mistake and only did it because they were forced to and Aunt May because they needed a cop out at the end of The Clone Saga regarding the fate of baby May Day and the "May's still alive" line being about Anut May instead was the best they could come up with. Mattie, Madame Webb, and the Hobgoblin haven't been dead long enough for us to see if it'll stick).