Jenna Maroney has one on 30 Rock. Or rather, had one. She's terribly upset to find out that her stalker has moved on, treating it as if her actual boyfriend had left her. Kenneth cheers her up by stalking her instead.
In The Adventures of Brisco County, Jr., the shy, bookish lawyer Socrates becomes the object of a crazy woman's affection, but he can't get police protection because they won't believe him.
In the recent adaptation of Sarah Waters' Affinity, a brand new character called Theophilius was drafted in as the heroine's wannabe suitor. Despite Margaret being a lesbian and mourning the death of her father, Theophilius wouldn't give up and insisted on pursuing her. He's finally written out when he tries to rape her, ranting about his belief Margaret's hung up on her father and saying he'll 'erase his mark' from her. What a freak.
Bad Girls: Di Barker, one of the prison guards, is a serial stalker, obsessing on numerous unfortunate men who pass through Larkhall. She steals their possessions, builds shrines and does whatever she can to break up their relationships. She receives her comeuppance when she's wrongly convicted for her husband's murder.
Leoben is Starbuck's Cylon Stalker with a Crush on Battlestar Galactica, keeping her trapped in an apartment with him for months and introducing a fake daughter. Starbuck keeps killing him, but he keeps coming back. She was understandably frakked in the head after being rescued.
Tully is arguably this for George in Being Human. He figures out George's general location by using newspaper articles, finds him in the woods post-transformation, and tracks him down to his home, where George finds him comfortably sitting in the living room. All because Tully is lonely and wants a friend (who he also bit himself).
Boardwalk Empire: Agent Van Alden towards Margaret Schroeder. He stole and sniffed her hair ribbon, specially ordered her immigration file for his own perusing, questioned her neighbor about her, and caressed, and later whipped himself to, a picture of her. Van Alden's boss even calls him out on his obsession with the Schroeders.
Booth on Bones gets saddled with a repeat offender of this. At the end of the episode, she accidentally shoots him while trying to kill Brennan.
Season one also has a stalker who fixates on Bones after his previous obsession dies.
They track him down later, still obsessed with Bones. They clear him of murder and he disappears after Bones punches him in the face.
Hodgins is this to Angela in the early episodes.
Spike from Buffy the Vampire Slayer. He became accustomed to following Buffy down the pavement or hanging around outside her house at night. He watched Buffy through her window, made a shrine to her, smelled one of her sweaters, and had a sex robot designed to look and act like her. Of course his little crush got a little less one sided in Season 6 and by Season 7 he became a little less evil.
Angel himself was one even before Angelus came about in Season 2. In Season 2's "Lie To Me", Angel shows up at The Bronze and even claims that he was hoping Buffy would show despite the fact that Buffy often attends with Xander and Willow. Also in Season 2's "What's My Line, Part 1", Buffy climbs through her window back into her bedroom. Somewhat creepily, Angel's already standing in there holding her stuffed pig, Mr. Gordo. It's clear he's been waiting for her to arrive. In that same scene, Angel admits to knowing about Sunnydale High School having its Career Week and explains his knowing about it as, "I lurk."
He doesn't seem to outgrow it too easily either. A whole episode in S4 was Angel stalking Buffy to keep her safe.
Even on spin-off series Angel, Angel actually at one point hires someone to watch her and this is years after their break-up. Aptly lamphaded by Spike:
Spike: Sending your lackeys to do your stalking for you. That is really pathetic.
Of course, it was essentially his job in the beginning to stalk her, handed straight to him by the Powers That Be in order to keep her safe, even though she was unaware of it for a while. That being said, however, it's a little disconcerting that when Angel falls in love with Buffy, he's hiding in a run-down car and she's wearing pigtails and sucking on a lollipop.
Angelus was also this towards Drusilla, stalking her before eventually turning her into a vampire after making her insane.
Early on, Annie's behavior towards Troy was like this, though she was too smart to get caught doing anything as obvious as stalking. This interest faded throughout the first season, especially as she started getting more chemistry with Jeff. Ironically, part of the reason her interest in Troy faded was because of Jeff giving her a "The Reason You Suck" Speech about it.
Jeff: High school must have been tough, huh? Waiting for a superstar to notice you. But here, he's all alone, and he needs so much help! Did you enroll in all of his classes, or were you worried that might freak him out? The important thing is that you are there for him. The important thing is that you are the only one there for him. And you don't really care what he wants, just as long as you don't have to share him with the rest of the world. Because really, you're just as selfish as I am. You're just not as good at it yet.
Dean Pelton's interest in Jeff is generally considered harmless. He went way over the line at one point (reading Jeff's email and basically blackmailing him into going on a date with him) but after Jeff pummeled him for it, the inappropriate touching and closeness continues. This may be because Jeff is practically twice the Dean's size and quite capable of beating him up, making his approaches seem less threatening.
David Platt from Coronation Street combines this with Psycho Ex. He just does not get the fact that Tina doesn't want to be his girlfriend anymore.
Jason Stickler from Cory in the House, who (mis)uses high-tech gadgets provided by his CIA Director father to spy on Meena.
Rebecca Bunch, the main character from Crazy Ex-Girlfriend, is obsessed with her old ex-boyfriend Josh Chan and sometimes "accidentally" runs into him, even moving across the country. However, this is also a deconstruction—Rebecca has legitimate mental problems, like anxiety and depression, and Josh reminded her of a time when she was happy. And Josh himself doesn't seem to mind, although he also seems oblivious to her feelings about him.
in "Somebody's Watching", the profilers figure a male Loony Fan is the one killing people connected to a certain actress, but the unsub turns out to be the actress's Psycho Lesbian friend.
"Broken Mirror" had a rogue FBI agent who was obsessed with a pair of twin sisters, one of whom he abducted, while "The Crossing" had a fairly generic stalker going after a woman he met while fixing her computer (they accidentally touched hands and she smiled at him, it was good enough for him). The rapist in "Aftermath" also learned absolutely everything he possibly could about his victims before going after them.
Johnny Smith of The Dead Zone gets one of these, of the Loony Fan variety, in the episode "Misbegotten". She's played for laughs in The Teaser, breaking into his house so she can cook for him, while Johnny blinks at her in bemusement. She gets a good bit creepier after she helps kidnap him, duct-tapes him to a chair, and nearly rapes him.
Episode 6 of Kieślowski's Dekalog, "Thou Shalt Not Commit Adultery". A 19-year-old postal worker is the Stalker with a Crush of a woman in his apartment building. This is shown as odd and unhealthy, but nonetheless a manifestation of a pure impulse to love. He explains that he no longer watches her when she has sex, for instance...
Dexter: Lila eventually becomes a version of one of these, going so far as to murder Doakes to protect Dexter's secret because she believes them to be soulmates, and eventually attempts to murder Dexter himself, as well as Cody and Astor.
After years of Foe Yay, the Master's first on-screen female incarnation has abandoned all pretence, outright calling the Doctor her boyfriend, sexually assaulting him when they first meet, and "jokingly" threatening to shoot him out of jealousy.
Sharaz Jek in "The Caves of Androzani" quite clearly has the creepy kind of hots for Peri, doing things like chloroforming her, stroking her face while she's unconscious, and carrying her around in his arms (again, unconscious) while whispering "so beautiful...so beautiful...". The fact that he also dresses entirely in black leather really doesn't help.
In Dollhouse, Alpha is one of these towards Echo. Disturbingly, he's even shown to sit naked in a room of a house in which he killed two people, watching a video of Echo. And later on it is revealed that Nolan is one for Sierra's original personality, Priya.
Steve Urkel on Family Matters found himself on both sides of this: for years he'd been Laura's stalker with a crush, then eventually found his own in Myra Monkhouse. Unfortunately for poor Myra, Steve was a more successful stalker than she was.
Scorpius's obsession with Crichton on Farscape has shades of this, and was deliberately played this way by Wayne Pygram. Crichton himself even lampshades it. Played with in that it's not so much Crichton himself Scorpius is obsessed with, but the wormhole knowledge he possesses.
Stark has a number of creepy interactions with Aeryn early in season three due to Zhaan sacrificing her life to restore Aeryn's. Word of God is that the intent was this trope.
Father Brown: The murderer in "The Crimson Feather" is revealed to be this. Having accidentally made a confession of love to the wrong woman, they killed her before the woman could humiliate them by revealing their obsession. A stack of unsent love letters addressed to their true object of desire was found in their room after they confessed.
Happens between a boss and an employee in Flashpoint where the employee became madly infatuated with his boss who did not return his affections. He repeatedly sent her emails and left gifts at her house. When she gently tried to tell him she wasn't interested and fired him as a result, he returned to the office with a gun so he could propose to her, believing he had a better chance with her, Completely Missing the Point of said firing.
Doctor Pilfrey spends most of the third episode of Fortysomething chasing after Estelle, acting on the e-mails that Edwin sent to him on her account, and turning his office into a love den complete with candles for when she showed up to see Paul. Similar tothe above, he turned out to be suffering from hypermania.
Niles towards Daphne on Frasier. At first Niles's hapless crush on Daphne was played for comedy, but he crossed the line when he convinced Daphne that a contractor she seemed interested in was a serial seducer of married women. Since this was before Niles and Maris separated it was very unhealthy behavior. Niles attempted to justify it by saying he did it for her "she deserves a doctor or a lawyer, someone for whom a T-shirt is an undergarment." (This statement was so appallingly elitist that if it was his real reason, it might have been worse.)
Glee: Rachel towards Will in episode 10. Also Suzy Pepper before her. Suzy's crush faded after she hospitalized herself, and she told Rachel to stop before she made the same mistakes.
Jacob Ben Israel. A stalker with a knickers fetish for Rachel.
Finn toward Rachel any time she's dating someone not him: in "Laryngitis" he accompanies Rachel to the doctor's surgery in order to instruct her to break up with Jesse because Jesse doesn't 'get her' as well as Finn does, then openly pervs on her as she gets changed behind a screen, and in "Prom Queen" he insults Jesse repeatedly and punches him in the face for slow-dancing with her at the junior prom—while he himself is supposed to be another girl's date.
Finn tried to punch Jesse but he has cat-like reflexes and dodged.
Also, Kurt's behavior towards Finn in the first season is a bit stalkerish. Kurt himself clearly doesn't see it though, as he thinks every attempt to call him out on it is due to homophobia.
Finn: The way you were all over me last year... if I did that to a girl, she'd take out a restraining order.
Kurt: You have issues with me being gay, I get it.
Finn: No, actually I don't. I have issues with the fact that you don't understand that no means no.
DaveKarofsky, anyone? He's way worse than any of the others. He's Kurt's homophobic bully and the crush comes out when Karofsky forcibly kisses a very terrified Kurt. Add to that the physical assault, constant insults and eventual death threat... it doesn't exactly go well.
Good Luck Charlie: Disney comes back to this trope time and time again. On Good Luck Charlie, another sitcom, there is Teddy, the main character. Her brother, has a friend named Emmett, who has a crush that's basically been built up by him into a full blown relationship with Teddy as his girlfriend. As usual per the Kid Com genre, it's played for laughs.
Gossip Girl: Chuck Bass's behavior towards Blair comes close to this at times.
As the last season reveals, the worst offender is, by far, Dan Humphrey, towards Serena, since he has been following her entire life for years, thanks to being the eponymous Gossip Girl.
Sue White on Green Wing will do just about anything to get with Dr. Mac... witchcraft, attempted murder, slander...
Guilt: Neville, who is seriously creepy, stole Molly's things and threatens Grace with a knife, but didn't actually kill Molly. He seems more mentally disturbed than actually malicious. We later see that he's been committed to a mental institution.
Will Graham acquires at least two of these in Hannibal, both of whom are serial killers. Although partially a result of his profession, Will seems to be attractive to killers who love his "pure empathy" and want him to understand them.
The first one, HannibalLecter, is obsessed with Will, talking about him endlessly with Jack, Chilton, and Bedelia. He even longs to be Will, bragging to Bedelia that he "gets to be" Will Graham in his new role as an FBI profiler. When gruesome crimes mirroring Will's alleged ones are committed in "Hassun", Hannibal makes thinly-veiled remarks attributing the killer's "love" for Will to himself, and questioning Will's unwillingness to accept him.
The second one, MatthewBrown, kills his friend in an attempt to prove Will innocent, hacks and rereads Will's files, seems to go out of his way to be the one who accompanies Will, and all this before he even talks to him. And then, when Hannibal assumes that he's only obsessed with Will because of his alleged crimes and attempts to tell him that Will's not a serial killer, Matthew states that he doesn't care.
In the series finale, it's revealed that Hannibal is in love with Will and everything he's done has been to bring him and Will together. It works.
Happy Days: Joanie had an early crush on Potsie, and later in the series Joanie was on the receiving end of an obsession from Fonzie's cousin Chachi. It was quite unwanted until even later when they became an item and eventually married in the series finale.
In Helix, after asking a series of increasingly personal questions in their various interactions, Dr. Hiroshi Hatake wistfully peruses an album of pictures of Dr. Julia Walker, both posed and taken from distances suggesting covert surveillance.
In Heroes, Sylar's developed this relationship with Claire.
Claire is on the receiving end again in Volume Five, this time from Gretchen. However, Gretchen comes clean a lot sooner, and Claire seems to have forgiven her.
The Chief of Police in Hill Street Blues had a really obvious crush on the police officer played by Mimi Kuzyk. He often made serious compliments to her, that were (in her opinion) too personal, such that it bothered her enough that she filed a Sexual Harassment complaint. Later, when she decided to leave the police force, the lack of the boss/subordinate power structure made her lose her fear of him, enough that they ended up Shipping and she moved in with him.
Homeland presents the Stalker with a Crush as the hero: Carrie plants hidden cameras and microphones in Brody's house, follows him, arranges to run into him when he goes to a support group for veterans, and otherwise stalks him. At some point in all this, she falls in love with him. Of course, she is a spy, so doing all these things does come with the territory, after all.
After being hit on by an 82-year-old woman albeit with syphilis in Season 1, "Informed Consent" and "Lines in the Sand" showed what a staggering age range of women are sexually attracted to House. 17-year-old Ali shows up at the clinic just to expose herself to him, calls him 15 times a day, wears low-cut jeans in front of him to show her thong (justified by the resultingEureka Moment), straddles his motorcycle while waiting for him in the garage, ignores most of Cuddy's threats to call the police, and locks herself in House's office. Subverted in the end by House telling that her she has a brain spore that causes loss of inhibition. Although it is rather heavily implied that he exaggerates the effects of said spore in order to make her give up her obsession.
House himself, sort of. The crush part is up for debate. House hires a private investigator to spy on Wilson when Wilson cuts ties with House, quits his job, and moves away. The PI accuses House of wanting to see if Wilson is pining, and he's right. House is clearly upset to discover that, despite having the PI set up bugs and everything in Wilson's car and home, Wilson hasn't mentioned House at all.
Lily's high school boyfriend Scooter cannot seem to grasp that Lily is happily married to her college boyfriend. He's mostly just a harmless, sad little puppy of a recurring character, but he seriously has revolved his entire life just around seeing Lily, and for some reason thinks he still has a chance.
In a non romantic variant, Patrice is kind of freakishly obsessed with Robin. Robin isn't precisely subtle about her abhorrence of her coworker, but Patrice is sort of obliviously half in love with her anyway.
"PS: I Love You" explores this and Stalking Is Love, and basically says the difference between being a stalker and being romantic is whether the stalkee is interested in the stalker.
Freddie in iCarly. He and Carly are really good friends, and the stalker side of things is pretty much limited to him waiting for her to come home after school by looking through his peephole (they live in opposite apartments), but it weirds some people out. Pretty much limited to Played for Laughs.
Freddie's stalker-ish behavior drops off pretty quick. If you watched the rest of the series, then watched the pilot, you wouldn't recognize Freddie as the same character. Of course, post-pilot, Freddie is hanging out with his crush most of the time with her consent, so it would be a little difficult to stalk her at that point.
The Mandy character seems to be a better fit for this trope.
Nevel. Oh boy Nevel. He has a wall of monitors solely for the purpose of showing slow motion close ups of Carly. Creepy.
Charlie towards the Waitress on It's Always Sunny in Philadelphia. Charlie uses pennies he's found to pay for people to spy on her. He also proposed to her once, she said no. The Waitress has a restraining order against him. But all he has to do is bring up Dennis and she's too busy thinking about Dennis to remember she has any restraining order to speak of.
JAG: Dirty Cop Frank Coster in "The Stalker", not only stalked Mac, but killed her former boyfriend Dalton Lowne and kidnapped her.
Jessica Jones (2015): Kilgrave is obsessed with Jessica, and ever since she escaped him has been searching for a woman that he enjoys tormenting as much as he did her. When this fails, he starts going after those closest to her in order to get her to come back to him.
In a Law & Order episode, one of these kills a woman's husband in what nearly everyone thinks is an accident, and then marries her. They even have a child together. But the late husband's mother wasn't fooled.
Used on Law & Order: Special Victims Unit with quite a twist: a cellist is attacked and continues to get threatening messages before being shot. The detectives find the man who's been stalking her, but he claims never to have attacked her. It turned out his landlady also insanely believed herself to be in a relationship with the stalker, and she threatened and shot the girl out of jealousy!
Ben in Lost is like this with Juliet. He keeps her on The Island against her will for 3 years, and gets her lover killed ... and then shows her the body out of pure spite.
Craig to Lois in Malcolm in the Middle. He even bought a house that was situated where he could peer into Lois's backyard from his window through binoculars.
Simon gets one of his very own in the second series of Misfits.
Monk: In "Mr. Monk and the TV Star," Monk ends up nailing actor Brad Terry for murdering his ex-wife with the help of an obsessed fan named Marci Maven, and accidentally transfers the stalker crush to himself. In "Mr. Monk and His Biggest Fan," we see Marci's new obsession with Monk has grown to extremes: she has a partially accurate diorama that is supposed to depict the carjacking scene of "Mr. Monk and the Three Pies", she has plastered the walls of her house with.
A victim of the week in Motive seems to be the "other woman" engaged to a pilot who's already engaged to another woman. She's seen wearing his family's wedding ring and photos of them together. However, when arrested for her murder, the man reveals that they only sat next to each other on a plane ride and the woman invented the entire relationship from there. She stole the ring, photoshopped images of them together, assumed he was only marrying another woman for money to support them and even tried to push the real fiancee down a flight of stairs. When the pilot confronted her on the delusion, she attacked him and he killed her in self-defense.
C.C. Babcock from The Nanny has borderline Yandere tendencies towards Maxwell Sheffield. Throughout the series, she's unable to grasp that Maxwell's not romantically interested in her. She gets better towards the end as she finds herself falling for Niles.
Abby from NCIS once had to deal with a stalker ex-boyfriend. His walls are covered with pictures of her (all taken from outside restraining order's limits), and the team assumes he's the one hacking into all her records. Turns out he was, but, he could only do it because a professional killer/hacker had already done it.
Nurse Jackie: After breaking up with Jackie, Eddie is taking a definite turn in this direction — befriending her husband and overdosing on tranquilizers to get himself admitted to her emergency room.
One Day at a Time: The 1980 episode "Endless Elliot," which centered on an awkward teen's attempt to court the series' chick daughter, Barbara. When Barbara tries to let him down easy, Elliot goes all-out to try to woo Barbara, and the result has her beyond annoyed. The rest of the gang comes up with a Zany Scheme to get him to go away.
By the way, the episode, which has been uploaded to video sharing sites, shows just how far times have changed. In 1980, all it takes is the zany scheme to make Elliot finally take the hint. This was before awareness of obsessive stalking, of which Elliot's behavior borders on, high-profile cases involving murder (e.g., Rebecca Schaeffer) and stalking laws were enacted. Today, Barbara would have Elliot arrested for stalking—or in the very least, have the police sternly warn him to stay away from her or face arrest.
Magnificent Century: Bali Bey to Armin. He climbs into her bedroom window after being turned down multiple times. And then acts surprised when she pulls a knife out and threatens him.
Season 4 has Psycho!Derek, a guy who stalks Peyton and gets closer to her by pretending to be her half-brother. The situation comes to a head in You Call It Madness, But I Call It Love, where he abducts her on the night of prom and keeps her Bound and Gagged inside her own house. It gets out of control when Brooke shows up- he promptly strangles her to subdue her, ties her up too, and then decides that since Peyton and Brooke had gotten into a severe fight, the best way to win Peyton's affections would be to murder Brooke in front of her. The girls barely escape with their lives.
Another stalker shows up in Season 7/8: Katie Ryan, Identical Stranger to Clay's dead wife Sarah. When she can't convince Clay to leave his current girlfriend Quinn to date Katie, she proceeds to invoke Murder the Hypotenuse and If I Can't Have You... by shooting both Quinn and Clay. They barely survive, and Katie isn't dealt with until the S8 midseason finale, where she comes back to try to murder Quinn again, and fails.
In the Only Fools and Horses 1993 Christmas special "Fatal Extraction", during a brief split from Raquel, Del sets up a date with Beverly, the receptionist of his local dentist, but calls it off after Rodney manages to talk him out of it. In the following days, Del sees Beverly wherever he goes, and starts to believe that she's stalking him. In a subversion, it turns out that their meetings were coincidental, and Beverly actually believes that Del is stalking her. She thought the date was a bad idea to begin with and didn't mind it being called off, but Del's threatening behaviour when he confronts her actually motivates Beverly into taking revenge by selling Raquel an answering machine which had Del's message about cancelling the date on it.
Morello in Orange Is the New Black. She went on one date with someone named Christopher, and then started to stalk him, ultimately going to jail planting a homemade explosive device under his actual fiancee's car, all the while telling everyone that he was her fiance. Later, she drives to Christopher and Angie's house using the prison van while they aren't home, and then takes a bubble bath while wearing Angie's bridal veil, and steals a little teddy bear from their bed. Later still, she gets a new boyfriend, and tells him that Christopher has been writing her creepy letters, and gets him and his friends to beat up Christopher at his home.
Suzanne (at that point, known only as "Crazy Eyes") became this to Piper in Season One, following her around, and even urinating in her cubicle as a sign of affection. Later, Suzanne gets a SWAC of her own, in the form of a fan of her Time HumpRomance Novels.
Ryan O'Reily was this way with Dr. Nathan. After she helped him through cancer, he immediately divorces his wife. Later, he forced a kiss on her, paid a fellow inmate to steal her stethoscope, and when she started ignoring him, had his brother Cyril kill her husband. After she was raped, he very quickly murdered the man that did it. It was even said outright that his love for her was more of a stalker obsession. The weirdest part about it: Dr. Nathan actually falls for him in the end.
Chris Keller as well. Such was his obsession with wanting to remain in Beecher's life even though Beecher repeatedly told him that he didn't want anything to do with him anymore.
Nathan/Lyndon from Pretty Little Liars develops an obsession for Maya, following her all the way back to Rosewood. When she notices this, she hides in the Khan cabin. It didn't help her, as she was later found, and killed, by him.
In one episode of the short-lived Probe, Austin is pursued by a stalker who murders one woman and tries to murder another she sees as an obstacle to her obsession with Austin. The twist? The stalker is a mentally enhanced orangutan.
Hoyt of Rizzoli & Isles develops a peculiar fixation on Jane and preys on her. He also wants to kill her because he likes that he thinks she's equal to him in some ways.
Also Adrian has had behaviors bordering on this to Ricky in Seasons 2 and 4. Tom to Adrian. Jack has shades of this in his behavior to Grace. Grant transferred schools to get closer to Ashley in Season 3. Ashley to Ricky in Season 3. Dylan has behaviors like this to Ben in Season 4.
On Seinfeld, Elaine was very prone to getting these.
Joe Davola had a Stalker Shrine made of pictures he had taken of her without her noticing. Naturally this creeps Elaine out. He later becomes suspicious and thinks she cheated on him. This causes him to run around searching for her and Jerry dressed as a clown.
Sherlock: Moriarty seems to be this where Sherlock is concerned from the very first episode onwards, as it turns out that the cabbie in "A Study In Pink" and The Black Lotus in "The Blind Banker" were sent to 'test' Sherlock's skills and to see just how good he is at his job as a consulting detective and Moriarty's arch-nemesis; his first words to Sherlock (albeit through another's mouth) are "Hello... Sexy".
Sketch (towards Maxxie) from the second season of Skins.
Emily is kind of this towards Naomi in the third season, but she's far too nice and likable (her pursuit of Naomi is more lovestruck puppy than Psycho Lesbian) for it to be creepy. Naomi declares her to be "very annoying" when she manages to break into Naomi's bedroom (not hard, since Naomi's mum has turned their house into a hippy commune), rather than pulling the all-out freakout that might be associated with this trope. But even so.
In the earliest days of Smallville, every other Monster of the Week had a crush on Lana. For that matter, Clark does the same thing to Lana with his telescope when she still lives next door to him.
Lana:(looking through the telescope) Did you know you can see my house from here? Clark:(acting innocent) No... Really? (moves the telescope to point somewhere else)
There's Also Alicia Baker, a girl with teleporting powers who did this to Clark. She eventually got better and one season later the two dated for real until Alicia was killed by a man who was framing her for crimes that he committed. Clark was not happy about that.
ATF Agent Josh Kohn for Dr. Tara Knowles in Sons of Anarchy. It does not end well for him.
The show Stalker of course contains these, though it also has plenty of the other kind as well.
Fifth from Stargate SG-1 cranked up the creepiness factor by declaring his love for Carter. This love led him to inflict Replicarter on the galaxy.
Samantha Carter seems to attract these types. Orlin and McKay both nurtured (relatively creepy) obsessions with her. Several others, much creepiers, have died.
Gordon Walker becomes this over the course of his first appearance for Sam and Dean Winchester, as he repeatedly tries to distance Dean from Sam. In each subsequent appearance on the show, his obsession with Sam becomes more pronounced and when he's turned into a vampirehis first instinct is to find Dean and Sam so that he can kill Sam.
And let's not forget Sam's own Stalker with a Crush Becky Rosen, who initially is not too bad since it's Played for Laughs, but in Season 7 she actually kidnaps him and drugs him with love potion, all while fooled into a deal with a demon.
Timecop: 1950s Hollywood actress Rita Lake from "Stalker" has two. One of them is Ian Pascoe, a recurring villainous time traveler who decides to impersonate her boyfriend and murder her. The second turns out to be the homicide detective who's investigating the case, as he's the one who offed all her previous boyfriends so he could have her for himself.
Sam Merlotte, in Season One. Thankfully, he got better.
Rose on Two and a Half Men is a bit odd in that she's both quite self-aware of what she's doing, and is actually on friendly terms with Charlie and his family. This is justified as not only is she a nice, helpful person who happens to have some obsessive tendencies, she's also highly intelligent with a PhD in psychology.
Her father, Harvey, was known to show the same behavior. Harvey had a one night stand with Charlie and Alan's mother and began to stalk her in the exact same manner that Rose stalked Charlie.
Wire in the Blood: in "Nothing But the Night", Tony Hill has a brief conversation on a plane with a woman. Her erotomania over the course of the episode escalates to the point where by the end, he comes home to find her in his house cooking him dinner and acting as if they're already married.
Harper has a huge crush on Justin, sometimes bordering on obsession. Alex even takes advantage of this fact, when she tries to break the temporary connection that formed between Harper and Justin, telling Justin that Harper watched him once, while he was sleeping.
A more serious and frightening example is Mason towards Alex.
In The X-Files episode "Milagro", Mulder's loner neighbor turns out to have a scary infatuation with Scully. He moved next door to Mulder in an attempt to get closer to her, he knows everything about her...even the novel he's writing is about her falling in love with him. Of course, in addition to being a stalker, the book he's writing has a villain who lives outside the book and tries to kill Scully.