Bakuryuu Sentai Abaranger: A borderline case is Dr. Mikoto Nakadai, the man is a super smart surgeon who was so bored with his life, that when he became Abare Killer he joined the Evolians and use his powers to what he consider as good use. In which case he formulate his own evil plans that are close to working and make the old villains look comical. It doesn't help the fact that he had a shard of the Evolian god Dezumozorlya.
Breaking Bad: Walter White has become this by the end of Season 4: He's charming, or at least Faux Affably Evil, doesn't even think twice about poisoning a child or using an elderly neighbor to check for traps at his house in "Face Off", and in Season 5 threatens to have his wife Skyler committed if she gets in his way. As of "Confessions", he is now blackmailing Hank to keep him from continuing with the Heisenberg investigation.
Todd is an almost perfectly textbook example of Antisocial Personality Disorder. He appears to be polite and charming but its mostly just because he's emotionally hollow. He murders a kid in "Dead Freight", later describes it as "shit happens" and doesn't seem to understand everyone's objections. He shows a similar lack of empathy or even caring when he murders Andrea in "Granite State" and tortures Jesse in "Ozymandias".
The Cousins are emotionless hitmen who kill everyone in their way, including innocents who didn't need to die, without flinching.
Encounters a "pure psychopath" about once a season. Interestingly, despite the hundreds of cases the BAU have investigated, only 9 characters have been listed as genuinely sociopathic/psychopathic. They are Adrian Bale, Nathan Harris (who was not actually a criminal), Frank Breitkopf, The Boston Reaper, Ray Campion, Raymond Donovan and Sydney Manning, Danny Murphy, and Greg Phinney. Of these, The Reaper is probably the worst, being an utterly amoral psycho who killed people for no better reason than a desire for fame, and went after the police when they dared to try and stop him.
Jeremy from the Season 6 episode, Safe Haven is a 13-year old "budding psychopath", with severe attention deficit problems and antisocial tendencies. He can't pay attention to anything for more than a few minutes, has a serious lack of impulse control, lies complusively and convincingly, killed his neighbour's dog, regularly tortures his little sister, and tried to poison his entire family with rat poison in the Thanksgiving turkey. After being abandoned by his mom he goes on a cross country killing spree as he attempts to return home and murder her, killing entire families and torturing the mothers. He has no real emotions (as is repeatedly demonstrated), but fakes them incredibly well, and at one point expresses a very creepy sexual interest in a girl who can't be much more than ten. Rossi suggests that they should keep him on file for a reason.
CSI: Crime Scene Investigation: Had a few of these as killers of the week. One possibility is the teenage killer in "Unsual Suspect" and "Goodbye and Good Luck". Another appeared on an earlier episode, and it was even lampshaded how she could switch personalities on a whim.
CSI NY: Had one, possibly two of these. In one episode, a young woman manipulated an older guy into killing a woman at a French Revolution themed party. Stella is annoyed that they can't prosecute the girl, because she didn't commit any actual crime, she just pulled the strings to get the other guy to act.
Dark Oracle: Omen appears to be one of these initially, but his genuine liking of Cally and slow development of human emotion keeps him from falling fully into the trope. Villain of the Week Claudia, who believes "if it feels good, do it," might well be a low-functioning sociopath. And then there's the comic book characters, Blaze (a hot-temperedJerk Ass who has no qualms about breaking a fellow student's arm), Violet (a Manipulative Bitch who enjoys scaring the crap out of her victims), and comic!Sage (who plays mindgames with Lance, screws around, and tries to off several girls with a poisonous snake).
Dexter: The eponymous Dexter Morgan, the most famous Sociopathic Hero and Serial Killer Killer on TV, is an example of a sociopath with a moral code his father instilled to direct his murderous urges at other killers. As such, he self-identifies as a sociopath but he usually only lies & manipulates his targets or people who are trying to hunt him down or to maintain a facade of normalcy (he initially gets into a relationship with Rita entirely as a disguise). With his Character Development, he's a hybrid of schizoid and sociopath who displays enough guilt, love and empathy to qualify as a reformed sociopath.
While this is how Dexter is written, it is important to note that real life Sociopaths don't and can't reform. The part of the brain that causes conscience and empathy does not work, and with no conscience they have no desire to reform even if it were possible. There will likely come a time that it becomes possible to get the conscience/empathy areas of a Sociopath's brain to work, it is unlikely that Sociopaths would consent to the treatment (which will create a controversy about the ethics of forcing it on them, given that it would make them morally redeemable).
Game of Thrones: Quite a number of these characters crop up, including (but not limited to) Petyr "Littlefinger" Baelish, King Joffrey Baratheon and Gregor Clegane.
Has a few among its villains, notably Arthur and Sylar. Elle Bishop was actually diagnosed as a sociopath and displays extreme aggression coupled with no empathy:
Elle: The shrinks diagnosed me as a sociopath with paranoid delusions, but they were just out to get me because I threatened to kill them.
It's also heavily implied that she wasn't naturally a sociopath so much as driven insane after her father had used her in various experiments relating to her power. She seemed to be growing out of it but never got the chance for redemption.
Bob Bishop most likely is one. Letting a sociopath raise a child to become a sociopath...
Sylar's own father is a case. When asked why he murdered Sylar's mother and sold him to another family, he replies that he doesn't even remember because "it didn't matter to me."
House: A memorable patient in one episode is identified as a Sociopath, by both the short hand and proper medical categorization. Notably 13 only recognizes her as such because she's terrified of her, with House saying it's a survival tactics, implying a common association with sociopaths to predator animals. Ultimately it turns out her apparent sociopathic behavior was actually a side effect of some other unrelated medical problem, and she "reforms" by the end of the episode.
Nora Dershlit. The only thing she cares about is to make friends, but her perception of what counts as "friends" is so horrifically skewed that she believes locking the iCarly gang in her basement against their will qualifies, ignoring their repeated expressions of the fact they don't even like her, believing she can force people to be her friends. She has absolutely no remorse for holding people against their will and outright tries to murder Gibby when he comes to save the iCarly gang. In her second appearence, she once more holds them against their will by holding Spenser hostage and torturing him on a giant wheel to keep the iCarly gang under control, even implying she can and will kill him if it comes to it. She also shows the Manipulative Bitch qualities of the trope, feigning remorse for her actions to trick the iCarly gang into agreeing to release her from prison and luring them into her trap again. She's also confirmed to be a sociopath In-Universe, even referring to herself as one:
Carly: Nora... You're a nutcase!
Nora: The correct term is disturbed, lonely sociopath.
The largest example of this trope would be Sam Puckett. She fits most of the signs without the torturing animals part.
Every character is a sociopath. They're frequently doing things that are unethical if not illegal, stabbing each other in the back, and no one in the gang is able to stick to a plan.
Dennis deserves a special mention. Some of his actions even leave the rest of the depraved gang disgusted. In one episode, Dennis accidentally admitted that he has no feelings.
He also shows more of the symptoms then the rest of gang. For example; Dennis has the superficial charm, fans sometimes comment on how he seems the most normal yet turns to be the most depraved of them all, plus he's good at getting chicks sometimes. He also seems a very cold calculated yet shallow understanding of human emotion. For example, Dennis' technique to get women (the D.E.N.N.I.S. system) is very cold and calculated but also very unsympathetic and fails to work at the end of the episode. Dennis also has the grandiose sense of self-worth that is sometimes played along with this trope.
The Kill Point: Mr. Rabbit, who manages to be the Token Evil Teammate of a bank robbing crew. He beats the hostages unprovoked, psychologically tortures one of them for no particular reason, carries around the severed ear of an Iraqi soldier he previously tortured to death, and tells Captain Cali that he considers the hostages "cattle" and "sheep being led to the slaughter." He ends up getting beaten to death by the leader of the team, because Even Evil Has Standards.
Had a serial-killer prostitute (based on Aileen Wuornos) who displayed the "cocktail personality" where she'd become a troubled mentally-frail patient for the psychiatrist or a seductress for Detective Stabler. Her son was the only thing she cared about and it turns out she killed his mother and kidnapped him as an infant.
One doctor did point out that not all sociopaths are evil unrepentant killers, most of them live normal lives like everyone else in their own way.
Malcolm in the Middle: Francis qualifies. Early on in his life he deliberately set a teddy bear of his on fire by dousing it with lighter fluid. During his childhood, after Reese and Malcolm were born, he frequently tortured them, stole their toys, locked them in a closet, and presumably scarred Reese on the shoulder with a bayonette. Probably one of his greater joys is tormenting his own mom. During his teen years, he also frequently made destructive revolts for no reason outside of just for the heck of it or simply to spite his mother. One instance of this is his stealing a neighbors car and then proceeding to total it. He also frequently smoked, did drugs, and slept around, also getting four nose pierces just to spite his mom, who said that she'd put him in military school if he goes so far as to get one. He seemed to become more sane when he joined a Dude ranch, but he then reverted back after he was fired, and it was implied in the season finale that the reason why he got a steady job and wanted to keep it a secret was to further anguish his mother about being jobless for his own entertainment.
Merlin: There's a good chance that Mordred is one of these. He is a rather unemotional child, seems quite apt at manipulating the adults around him, shows no remorse when he kills several armed men, and responds with anger rather than grief when his father is executed.
Person of Interest: Root demonstrates all the clinical symptoms of this (pronounced Lack of Empathy, lack of proper understanding of morals, etc.). The scary thing is that she claims that she isn't one, but she wishes she was so that she would have an easier time doing what she's doing. Perhaps the clearest sign she isn't a sociopath was the affection she had for her friend as a child and her decision to take revenge on the man who killed her.
Shaw zigzags this, showing no emotion at her father's death as a child, preferring violence to other solutions, and even confessing to one PoI that she feels no emotions aside from anger. However in the same episode she clearly begins to empathize with the girl and won't seek medical help until after she's saved her. The girl claims to have figured out Shaw: That she does feel other emotions, but they're muted in comparison to normal people.
Sergeant Will Strausser, at least as of "Sex and Drugs" is being deliberately set up as one. "Ties That Bind" has Miles Matheson and Strausser discussing the fact that Strausser is one, with Miles pointing out that Strausser was going to be put in a padded room before the blackout happened. "Nobody's Fault But Mine" has Strausser threatening to rape Charlie Matheson to Rachel Matheson's face, and he actually tries to rape Rachel when it's just the two of them alone. Fortunately, Rachel manages to kill him off.
Miles on occasion is hinted as this.
Sherlock: The eponymous character's Arch-Enemy, James Moriarty, is this trope played very straight: he has no empathy whatsoever, is a liar, charmer, and manipulator who easily surpasses Sherlock in all three departments, is a criminal mastermind who has orchestrated scores of crimes—up to and including murder—throughout Europe merely because he was bored, and by the end of season 2 has single-handedly wrecked Sherlock's credibility, career and relationships. The difference between the two is probably best underlined when they first meet face to face.
Sherlock: People have died. Moriarty: Oh, come on...that's what people DO!
Lx-3, Lex's clone and Shadow Archetype from Season 10's "Lazarus" is a solid example. He spends all his time on-screen committing mass murder, has a Hair-Trigger Temper and a sadistic streak, seems to actively enjoy murder for its own sake, and hates everyone. He tries to kill every person he meets.
Bob Rickman, corrupt salesman with Mind Control powers who has no qualms making his enemies kill themselves or brainwashing innocent people to kill for him. His pesticide plants were massively toxic, spreading cancer and environmental damage, which he took delight in being able to get away with thanks to his powers.
Sam Winchester exhibits classic sociopathic behavior when he loses his soul in season six. Though he becomes an example of a pro-social version, as his interest in hunting remains constant.
This trope doesn't apply to most of the show's monsters or villains...with the exception of the Leviathans. They're a species comprised of nothing but sociopaths.
The Wire: Marlo Stanfield. Unusual in a show well-known for it's Gray and Grey Morality, where even the most hardened criminals are capable of kindness and are often shown doing ordinary things. A ruthless drug dealer, Marlo has no qualms and seemingly no moral compass. One of his defining moments is when he was a security guard with a family killed...just because. He is also the most prolific criminal on the show, with over a dozen victims to his name. His personality is remarkably reminiscent of a Serial Killer.
Kings has Andrew Cross, who makes for an ugly contrast with the narcissists who compose the rest of his family. A bored, listless young man who admits to viewing other people as things (and doesn't seem to understand that this is wrong), Andrew displays a very limited emotional affect, moves impulsively from idea to idea, and has some very troubling sexual urges, as evidenced by his stalking of his aunt, and his leaking of his cousin's nude photos to the press. In the end, Andrew sides with his father's coup, only to betray him to his uncle Silas when it fails, and then, in the closing scenes of the show release Vesper Abaddon from prison with no prior explanation, all with the same perpetual bored look on his face. Whether Andrew has any genuine goals, motives, or loyalty in him, is left in serious doubt as of the end of the show.