Sierra in Total Drama definitely qualifies as this to Cody, smelling his shoes, sucking poison out of him, and knowing everything about him to the point where he develops a phobia of her. Heck, this trope should be called "The Sierra."
Half of this could be because she is a Loony Fan...a little too loony, as Heather has noted.
After Sierra tells the cast something about Cody she wasn't even present for:
Courtney: "How did she even know that?"
Chris: (to Sierra) "The things you know... scare us. Seriously."
Izzy's biography claims she stalked boys as well. Apparently she threw one down a sewer when she got sick of him.
Sponge Bob Square Pants: The episode "That's No Lady" has Patrick dress up as a girl named "Patricia", leading Squidward and Mr. Krabs to fall in love with "her" and act like complete stalkers, popping out of random places (like the sink and the fryer) to ask "Patricia" out on a date. And they still persist even after Patrick continues to tell them "no".
In the episode "The Two Faces Of Squidward" the entire town act like stalkers towards Squidward after an accident causes him to become very handsome.
Spongebob's Ho Yay-ish actions towards Squidward carry undertones of this.
Looney Tunes: Pepe LePew — and it doesn't matter if the cat is male or female (and 1947's "Scent-imental Over You" showed us that it didn't matter if it was a cat, because the object of Pepe's affection in that short was a chihuahua who glued skunk fur onto her body so she can be like the other dogs), so long as she (or he) is painted like a skunk. And the DC Comics version of Looney Tunes had Pepe go after a black bull (the one who squared off with Bugs on "Bully For Bugs") with a white stripe and several human women who in one way or another have black and white skunk stripes on them. Can we say "Anything That Moves," boys and girls?
Pepe: (at the end of "Little Beau Pepe") Why is it that whenever a man is captured by a woman, all he wish to do is get away?!
In the Bugs Bunny cartoon, "Rabbit Romeo", Millicent an overweight and ugly Slobbovian rabbit is like this toward Bugs. Bugs is eventually able to turn the tables and steer Millicent onto her caretaker Elmer Fudd!
Tiny Toon Adventures: Fifi LaFume, much like her predecessor Pepe, only she's never had to fight off guys chasing her (in fact, she prefers it).
Except if its Elmyra chasing her.
Ed, Edd n Eddy: The Kanker Sisters (the three trailer trash girls Lee, May, and Marie) towards the the Eds in a very over-the-top fashion.
Hey Arnold!: There are several hints that Helga's comedic stalker, Brainy, followed her around because he had a crush on her. In the one episode when, instead of punching his lights out, she finally asked why in the world he's always lurking behind her (and how he finds her), his only response was "I like pain." to give her a ring.
But that's nothing compared to Helga herself. She has a shrine, a bubblegum statue made out of his chewed bubblegum, and several books of poetry dedicated to Arnold, even though she treats him as badly as she treats Brainy.
And then there's Curly towards Rhonda.
In Justice League Unlimited, Carter Hall believes that he and Hawkgirl are destined to be together because they're the reincarnation of Thangarian lovers in ancient Egypt. Even though this is strongly hinted to be true, he still comes across as a Stalker with a Crush. Most of the Justice Leaguers (Batman and Green Lantern in particular) have not failed to notice this.
The "reincarnated Thanagarian lovers" thing is also subverted when it is revealed that proto-Hawkgirl ended up leaving proto-Carter for proto-Green Lantern. Yep, even destiny itself is telling Carter to buzz off.
Coop has the dig on for Yin in Yin Yang Yo, though his becoming The Mole for the Night Master isn't entirely to please her so much as he's tired of being kicked around.
In Foster's Home for Imaginary Friends, Berry's stalker-ish crush on Bloo becomes quite extreme, to the point she even tries to get rid of Mac so she can have Bloo to herself. The trope is clearly lampshaded in a subplot where the rest of the characters are deeply engrossed in a soap opera with a love affair that goes sour.
Myra Brandish of The Venture Bros. is the insane former bodyguard of Rusty Venture who believes herself to be the mother of his twins (this is heavily implied to be true) who breaks out of asylums once a year to antagonize the Ventures somehow, still being in love with Venture and obsessing over her (supposed) children.
Timmy of The Fairly Oddparents has two Stalkers With a Crush, both of whom have shrines and various Timmy merchandise. One of them, Tootie, is fairly sweet otherwise, but she comes on too strong for Timmy (possibly coming from the fact that Vicky is her older sister), while the other, Veronica, also routinely wears a wig while demanding to be referred to as her more popular friend. Yeah...
There's also Juandissimo, who is in love with Wanda, despite the fact that she is married to Cosmo.
Also, The Darkness in "Wishology" becomes obsessed with Timmy after he becomes the first person to put something good into it (i.e. light). In fact, all its action in Parts II and III were to capture him and keep him close to its heart... It wipes out Yugopotamia and captures a race of creatures just to do this.
Herbert. He could just be a creepy homosexual pedophile, though... his attentions aren't always spent on Chris, though Chris seems to be his main target.
Meg in the episode "Barely Legal" where she became violently obsessed with Brian after he took her to her prom, which included making a Stalker Shrine.
There was a one-shot character that happens to be Peter' old prom date, who has a hallway full of pictures of Peter. She is also wearing the dress that she wore to that prom...and hasn't washed the hand that touched Peter's since then...or flushed the toilet he used either, for that matter. Her explanation of everything is "It's a little piece of you that's kept your memory alive!" Squick Central...
Quagmire may hit on anything in a skirt but there are a few episodes that portray him as having an unhealthy obsession with Lois (despite that in "Jerome is the New Black," he names off "hitting on Lois" as one of the reasons why he hates Brian. Hypocritical Humor, much?).
To be fair, his issue is that Brian LIVES with Peter without providing a drop of money. (You know, 'cause he's a dog.) And Quagmire, tends to be more of a quiet stalker with Lois, only going after her when she and Peter aren't together. So he still does respect Peter.
To some extent, there's also Neil Goldman towards Meg.
The episode "Peter-assment" portrayed Peter's boss Angela as being one of these towards him.
Artie Ziff was this way to Marge in the later seasons of The Simpsons.
"I am watching you THROUGH A CAMERA!"
One-shot character Julia was one of these towards Homer in the episode "Homer Of Seville".
Elisabeth "Sissi" Delmas from Code Lyoko stalks and harasses Ulrich, her "sweetheart", almost every day, and is close to obsessed with finding out the Gang's secret. It gets to the point where, in the last episode, she goes as far as to attach a tracking device to Ulrich's coat (no word on where a fourteen-year-old schoolgirl got a tracking device, probably the Internet) to find out where he and his friends disappear to every day. It does work, but the trusty RTTP is there to reset it. The ex-Lyoko Warriors finally accept her as a friend after that to thank her for all the help she can't remember giving them, so we can assume that the obsessive behavior has stopped.
To some extent, William towards Yumi, though he's not nearly as obsessed. Only creepy. Especially as he never appears to hang out with or talk to anyone else on such a regular basis.
Vlad Masters/Plasmius in Danny Phantom fits this trope. It doesn't matter that Maddie is happily married with two children to Jack. He also has the trappings of this with Danny, though it's more a platonic than romantic (Sorry shippers...) which makes it creepier.
Kim Possible once spent an episode stalking Ron and Yori in their mission, due to her crushing on Ron and being jealous of Yori (a jealousy that included accusing Yori of being the Enemy of the Week).
DNAmy is definitely this towards fellow villain Monkey Fist.
Lorna from Carl Squared. Complicated by the fact that Carl's clone C2 is a little sweet on her.
Chowder: Panini definitely qualifies as Chowder's stalker. She watches him with binoculars, physically chases him around, wanted to have him legally declared her property, and for a brief period lived in his clothes.
The X-Men: Evolution version of Gambit seems to come across as this in the episode "Cajun Spice", after he ends up abducting Rogue in order to use her powers to rescue his father from a rival gang. The "stalking" and "crush" parts are unrelated initially.
Rogue: How do you know so much about me? Gambit: I've been watching you, Rogue. You're such an unhappy girl.
Blob also is this briefly, when he thinks that Jean's refusal to hang out with him is an insult (rather than simply that she has stuff to do).
Hexadecimal of ReBoot sometimes acts this way towards Bob.
The Creeper has a short yet extreme crush on Harley Quinn that causes at least one The Cat Came Back-like moment. Though we actually see him sniffing his way through the town, trying to follow her.
The Mad Hatter's creepily stalkerish behavior towards Alice!!!
In 1990's Spider-Man: The Animated Series there's Hydro-Man. The guy only ever shows up to chase Mary-Jane around. He was so obsessed over her that after his clone heard she may have died he forced Dr. Miles Warren to create a clone of her based upon his abilities. Didn't really work out for him; as she still loved Peter and they both died anyway.
Venom in The Spectacular Spider-Man, but it's a bit of a Love Triangle. The symbiote wants to be with Peter Parker, who it is mad with for rejecting it; host Eddie Brock is also mad at Spidey, but he teams up with the symbiote because he thinks it's the only one left that cares for him, even though he admits "it only loves me for the hate". In Brock's case it could be particularly bad because, since he knows all of Peter's secrets, he should also know why Peter appeared to act so irresponsibly and selfishly- he was in reality either busy as Spider-Man, or himself being corrupted by the symbiote. But he still feels alone so he keeps going back to the symbiote just so they can hate Peter together.
In the third season of Winx Club Nabu was a somewhat more benign version of this in the first few episodes he appeared in. He had run away from home in order to learn what the girl (Princess Aisha) his parents had arranged for him to marry was really like, and he ended up falling in love with her.
Unlike the video games, where his obsession seems to be solely with her power, Ganon seems to have some attraction of this nature toward Zelda herself in the animated Legend of Zelda. In one episode he abducts her and tries to force her to marry him; in another he declares to his minions, "I want that princess!"
Heloise in Jimmy Two-Shoes. The actual stalking part is largely not seen, since she's already friends with Jimmy, but she does have a Stalker Shrine hidden in her house. A one episode gag had Jimmy saying her name, having her pop out of a bush holding binoculars, the clear implication being that she was watching him.
Heloise herself has a stalker in the form of Peep.
Ice King from Adventure Time is one to any princess, but Princess Bubblegum is his main target. He even wrote a song about it.
Most of the love songs on The Amazing Chan and the Chan Clan are like this, but in a cute harmless way. Plus, they also seem meant to make use of the show's detective theme with titles such as "Undercover Man" and "Whodunit" so it's partially justified.
Phineas and Ferb: Before they became an Official Couple, Candace was something of this to the oblivious Jeremy. At one point she was even spying on him with binoculars (yeah, ok, from a few feet away, but still).
Candace even realized this in the first movie and stopped herself shortly before she and Jeremy hooked up.
Even though they're friends, Isabella is also like this with Phineas. The only usual reason she sees/helps/hangs out with Phineas and Ferb and go though their adventures together is only to get Phineas' attention (and to a much lesser extent, badges).
Katrina Rad in The Problem Solverz episode "Magic Clock". She starts out as a Loony Fan for the trio, but while following them around to write a blog entry about them, she escalates into a crazed Roba fangirl.
Katrina: Mm, Roba's shadow is so good lookin'... I'm gonna hug it!
Roba: Okay, now I'm really creeped out.
From what we've seen of Lola Bunny in The Looney Tunes Show, she seems to be this. In one of the Merrie Melodies segments, We Are In Love, she's shown standing outside Bugs' house... in the rain... with a Slasher Smile. The whole song is this trope.
Bugs' also mentions getting a restraining order, a home security system, and moving to Bolivia to escape Lola Bunny. All of which failed due to the difficulty of enforcing them, learning the system's code, and following him to Bolivia.
She tapped his phonelines and moved into his house in secrecy.
Ironically, when Lola's attention switches to Daffy, Bugs starts being attracted to Lola, and unwittingly plays along when she attempts to use him to make Daffy jealous.
Wackie Jacky from Kick Buttowski is this to Kick. Complete with a creepy room filled with his pictures.
Terry/Batman's girlfriend Dana gets one in an episode of Batman Beyond, though at first she thinks that the flowers and notes are from Terry himself. She doesn't take too kindly to being kidnapped, no matter how conscientious her captor is, then she finds out that she's not the first person he's stalked.
In Tom and Jerry episode "Flirty Birdy", Tom dresses up as a female eagle which entices a male eagle and leads him to chase Tom with amorous desire for the whole short.
Moe Syzlak on The Simpsons stalked the late Maude Flanders and other Springfield women; one of them placed a restraining order upon him.
Wolverine/Logan comes across as this in a number of episodes from the '90s X-Men as he hopelessly pines for Jean Grey, who, despite being at least somewhat interested in him, is adamantly loyal to her boyfriend, team leader Cyclops.
Ogo toward the titular Robot And Monster. He has done things such as taping pictures of Robot to the back of his eyelids so he sees him whenever he closes his eyes, and making a pillow out of Monster's fur.
Donatello to April in Teenage Mutant Ninja Turtles (2012). He stares at her from afar, knows very little about her, and had spent hours making a chart on every possibility April will throw at him.
It may diminish later.
Magpie to Batman in Beware the Batman. Though it initially starts as mild attraction towards him in her first appearance, she becomes obsessed with him when he pays visits to her prison to maker her feel less miserable. In "Attraction", she mistakes his partner, Katana, with his lover, and she breaks out to try to "rescue" Batman from her.