The Gotham City Police Department is corrupt, with the exception of Gordon, Renee Montoya and one or two more good cops. This becomes a major plot point in Gotham Central, a series set within the Major Crimes Unit of the GCPD, the only consistently honest branch of the department. Since its members are all personally selected by Gordon, they have a modicum of integrity and competence, but the universal corruption of the rest of their force makes even their simplest of cases difficult since the other units are stealing evidence, accepting bribes, and often committing the crimes themselves. This comes to a head in the Corrigan story arcs, where Jim Corrigannote Not that one (the dirty cop of the series) is selling evidence on the black market, redistributing the heroin that is collected by the narcotics unit, and eventually starts personally murdering other cops that are trying to stop him. At the end of the series, though everybody knows he did it, his web of corruption has spread so far that the case against him is sabotaged and he gets off completely free until Infinite Crisis Aftermath, where it comes back to bite him in the ass. The one-time Internal Affairs and the MCU are actually able to build a case against him, they have to compromise their morals and let him go to save one of their own.
Even the DCAU isn't immune. Harvey Bullock may have been more of a Cowboy Cop most of the time, but everyone agrees he went too far when he gave one of his Mafia connections information on a man in witness protection so they would kill him. The man in question shot Commissioner Gordon, but still. In his pre-Crisis origin, Bullock was a dirty cop, on orders from the mayor to sabotage Gordon's career, but then came to respect him.
Blüdhaven was even worse than Gotham. Criminals there who didn't share the profits from their crimes with the police were murdered. The police chief placed a bounty on Nightwing's head. The only truly honest cop — technically — in Bludhaven was Nightwing himself, who, in his Dick Grayson identity, joined the force in order to bring it down. (The city was eventually destroyed when the Secret Society of Super-Villains dumped the monstrous Chemo into the place; Nightwing, Robin, and Batgirl survived because they were lucky enough to be out of town at the time, and Tarantula was later shown alive, and but pretty much most of the other residents weren't so lucky.
In Batman: Zero Year, Bruce assumes the entire GCPD is dirty; no exceptions. After all, when he was a kid, he got taken home in a police car and saw a young Jim Gordon get "given" the trenchcoat he always wears. He thought this showed everyone liked the police and only realised the truth later. (He later learns that Gordon keeps the coat as a reminder that it's easy to give in to corruption if you don't keep your guard up.)
In Red Robin the murderous blackmailing GCPD detectives Roman Cavallo and Marcus Wise hire an assassin to kill Tim Drake when they realize he's going to publicly reveal them during a press conference for an outreach program he's overseeing. Tim was anticipating it though since he'd been researching their criminal activities and looking for a way to actually get them imprisoned despite their connections since he was still Robin.
The Batman Confidential story arc "Wrath Child" reveals that the original Wrath's father, who alongside his wife was killed in a firefight with a young Jim Gordon, was one of the corrupt cops in the GCPD and that to save his own ass and that of his fellow corrupt cops, a then-Captain Gillian Loeb covered up the incident and forced Gordon to go to Chicago.
Two-Face has several cops in his pocket in the Joker graphic novel.
Simon Dark's "brother" Tom Kirk was murdered for being a decentish but cocky cop who wouldn't listen to his corrupt superiors. The fact that he manages to come back without anyone the wiser to him having been dead, missing and experimented on makes it clear that his disappearance was covered up and those responsible were willing to treat his reappearance as him having gone on a bender. This is why he doesn't trust anyone in the GCPD (with work related things, let alone his secret of being undead these days) and refuses to work with a partner.
Comic Cavalcade: A Gotham cop gleefully arrests Locksley Smith for jaywalking when he hears the man complaining about his inability to avoid unlocking any lock within a couple of feet, and then brings him to a judge he knows will lock him up for it (or unlocking his handcuffs) when Locksley can't pay the fine. This of course leads to the gang whose cells he was locked up by all walking out of prison.
Elsewhere in the DC Universe, Hub City (where The Question is the biggest heroic presence, if you can even call him one) is even worse than both Gotham and Bludhaven. The FBI yearly analysis lists Hub City's police department as the most corrupt department in the country, and even the honest cops currently trying to improve the department have a bad history; the current straight-arrow chief only became a crusader for integrity because of what he encountered when he was out shaking down local criminals and businesses for the bribes they owed him.
Sensation Comics: In the Wonder Woman feature Ely Duel is the chief of county detectives while also making money as the masked criminal head of the Crime Combine. He uses his position to make arrests and get away with shooting those who are in his way.
In Superman Smashes the Klan, the old white cop flatly refuses to help Roberta when her brother is kidnapped, instead complaining about how Asian-Americans apparently have it easy compared to white folk. He's later revealed to be a member of The Klan and springs Matt Riggs from prison.
The Brotherhood in X-Men Noir, Chief Magnus' private task force dedicated to controlling the criminal element from within. Magnus is dedicated to the pursuit of justice, but as he says, "laws only work on the law-abiding."
Luke Cage Noir, meanwhile, has Officer Rachman and Tombstone, corrupt cops working for Randall Banticoff. Tombstone, in particular, was a gangster before (and after) he became a cop.
Nextwave: Officer Mangel is initially introduced as an upstanding member of the force who's about to fall victim to Retirony...and then we get several pages showing him beating up drug dealers for money, threatening prostitutes for money, and beating up a mugging victim because he still has some money left. He then gets forcibly transformed into a robot monster, blown up, kicked by Aaron and Tabby for being a cop, and handed over to his "friends" (victims) by an unwitting Monica, who promptly kill him.
Dirty Cops are a big factor in Frank Castle becoming The Punisher. The criminals who killed his family worked for the Costa family, and Frank was able to identify every one perfectly; unfortunately, the cops — at least the ones he went to — were clearly being bought by said mob. (This is also a big reason why the Costa Tannen family is no longer a presence in the Marvel New York underworld; he went after them first.)
In Ultimate Spider-Man, Jeanne De Wolfe was secretly working for the Kingpin of Crime the whole time she acted as Spidey's Commissioner Gordon, and was possibly his lover.
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The Archies encounter one in "Trap City, U.S.A."; while driving through a small town, their van is pulled over by the sheriff for speeding — they weren't, but the sheriff works on commissions, so pulls everyone over for a fine. He's also the judge, so fighting the violation in court's no good. The Archies are forced to do a concert to pay the fine, but manage to get back at the sheriff when Veronica spots her uncle, the state governor, in the audience, and tricks the sheriff into making an Engineered Public Confession while Uncle George is listening. The story ends with the ex-sheriff hitchhiking out of town, at which the Archies offer him a lift — for a fee of $12 a mile.
In the Astro City "Dark Ages" story arc, Charles' partner Lannie takes weekly bribes from the criminals to overlook their activities. Charles refuses to get involved, rejecting the bribes but refusing to report Lannie to Internal Affairs. He gets shot in the back as a result.
In Baker Street, corruption is rife among the London police, with Sharon's ex-husband having been a dirty cop. In #2, Sharon sees a uniformed constable dealing drugs to a punk and is visibly disgusted.
Disney Ducks Comic Universe: There have been at least two stories where the Beagle Boys were shown to be in charge of the Duckburg police force. In the first, it was part of an Alternate History where they changed occupation because Scrooge had already lost his fortune, and in the second it was just part of a weird-ass nightmare that Donald was having. Also, in the former example, they said Donald could buy his way out of a ticket.
In Drowntown, Grace Carter used to be a detective, but became disillusioned (like Leo, the protagonist) and started working both sides (not like Leo). When the story begins, she's trying to eliminate Leo because he knows all about her.
Ghoul Goblin: The sheriff of Boon Hill is described as a "go along to get along" sort of officer, who puts more stock in town politics than in justice or the law. He spends the majority of the story being a pain in Harry's ass and obstructing his efforts. Later on Harry is merely standing nearby when one of the Talbots is run down by a big truck, and since Harry's an out of towner without local connections the sheriff decides to arrest him for it.
Ciudad Barranquilla, the primary Mega City in South America, is even more of a craphole than the Mega-City One police state in North America, being completely run by a corrupt Justice system which operates more like a mob by killing anyone they want, letting criminals run free, and extorting the poor majority living in the projects.
Even the Big Meg's judges aren't immune to this trope. The entirety of "The Pit" arc has Dredd assigned as sector 301's Sector Chief in order to weed out dirty judges on the take from the Frendz syndicate. It turns out that the dirtiest judge in the Pit is the sector's head of the SJS. Dirty judges are so commonplace a problem that there's an entire penal colony devoted to holding judges convicted of corruption on Titan. (The standard sentence for corruption is twenty years hard labor on the Titan colony.)
When he was still a human Street Judge, Judge Death was in league with a drug gang whom he eventually executed for holding out on him and to seize their product for himself and his men. While he otherwise had a happy career executing citizens for jaywalking, it doesn't pay the bills.
The storyline "In the Event of My Death", featuring a war between Mega-City's organised crime gangs, has Dredd concerned that they seem to know more about the Judges operations than they should. It turns out Judge Hart has been on the take for twenty years, revealed to the reader when one mid-level gangster is delighted to see him during a crackdown, and he has to kill both the criminal and a fellow Judge to keep it quiet. He's not the main sorce of information, though; that's a psychic who can infallibly track Dredd's movements.
The Simping Detective has Jack Point effectively caught in the middle between the local mob and Sector 13's Sector Chief Daveez, who is effectively a mob boss in a judge's uniform. One character notes that Jack is the only honest judge in Angeltown.
Ric Hochet had its fair share of corrupt policemen. The very first villain of the series, Chameleon, was one. He joined the police just to get revenge on the cop that sent his father to jail. Bex Turner was a mirror match to Ric Hochet, as both are very similar physically and intellectually.
Robyn Hood: The sheriff of Robyn's hometown is in Oswald King's pocket, and covers up Oswald's son Cal's crimes; including his rape and assault of Robyn.
In Sherwood, Texas, the Sheriff of Nottingham County is in the pocket of the local gangs. As the story is a Setting Update of Robin Hood, it should not surprise anyone that the Sheriff is corrupt.
Almost every damn cop in Sin City, with the notable exception of John Hartigan. The police commissioner is in the employ of the powerful Roark family, showing up personally to ensure that Marv takes the fall for Cardinal Roark's crimes. But Hell and Back shows that even he can be pushed too far. Dwight notes offhandedly that there are some honest cops on the force in The Big Fat Kill, but that they are extremely rare.
Simon Says: Nazi Hunter: Erhardt Rohr is a former Nazi-turned-chief-of-police in Germany. He's still every bit the sadist he was in the war, and still hates Jewish people.
