Green Lantern and Hawkgirl. It starts off as subtext, with them alternately bickering and rushing to each other's rescue. It grows to the point that the Joker, watching Hawkgirl and Green Lantern deal with one of his booby-traps, feels the need to comment on it.
Joker: Whew! Is it just me, or is there something going on between those two? "Will Green Lantern ever admit to his feelings? Will Hawkgirl ever stop sublimating her passions with that big honking mace? Will true love conquer all?"... Not on my show!**Boom!**
The episode ends this with blatant obviousness for a cartoon. After the UST is resolved, we hear an offscreen voice say "It's about time!" — and then a cut to a woman winning the jackpot at a slot machine. Hmm...
Also blatantly stated at by their Alternate Universe, where John even states they are sleeping together.
The resurgent UST between Green Lantern and Hawkgirl, and between Green Lantern and Vixennote who Lantern started seeing while Hawkgirl had secluded herself in the aftermath of her Heel–Face Turn in Starcrossed was Left Hanging at the end of the series. However, it's confirmed in a trip to the future that they eventually have a son together, Warhawk.
Batman and Wonder Woman. However, it's more or less only unresolved on Batsy's part, due to his... "issues". Wonder Woman is very open, even aggressive, about her desire to get together with him. A comic published at the same time plays with the same concept, but goes further by showing what life would be like if Batman and Wonder Woman got together. The tension is so strong that even when they were turned into children by Morgan Le Fey, their attraction was still noticeable.
Kid Green Lantern:(to an oblivious Superman) You know, for somebody with like fifty different kinds of vision, you are so blind.
Code Lyoko. Ulrich and Yumi (used to be the picture of this page). To a level at which all Western Animation examples will be compared. This couple may live on in infamy as the only one to ever sit half-naked in a heat bath together at 4 PM on Cartoon Network. And still not hook up. It takes until the last few minutes of the last episode of the series before there's any kind of resolution, and even then it's only a tentative "they will". It seriously borders on Mind Screw.
Kaeloo and Mr. Cat's relationship absolutely reeks of this. Their attraction to one another is painfully obvious, even to the other characters, who also happen to have had a few moments with the she-half of the budding couple.
Kimiko and Raimundo from Xiaolin Showdown, especially in the episode where Hannibal Bean intrudes Raimundo's head. He rests his arm on her shoulder in the cinema (only to find out that she is, in fact, Hannibal). However, since they never get together in-show, fans are left to guess on their own if it was resolved post-Grand Finale.
Eduardo and Kylie from Extreme Ghostbusters. The two have a love/hate relationship going since meeting in the first episode. Many clues were given, such as when they went out of their way to save each other and most notably when Eduardo had an intimate dream about Kylie. Unfortunately, the show was canceled before there was any resolution. Darn.
In Young Justice: The Animated Series, Superboy and Miss Martian have a lot of UST... until episode 11.
More so with Wally and Artemis...until the end of season one.
Robin and Starfire from Teen Titans (2003) finally hooked up long after their mutual feelings were known to their teammates, their enemies, and random nerds on the Internet (in-show). This is based on a storyline in the comics.
In Iron Man: Armored Adventures, especially in the new season seems to be filled with UST between Pepper and Tony.
Spoofed in an episode of American Dad!, where Haley says that Stan and Roger's rivalry over who's the "big dog" is due to UST and that they should just fuck already and resolve it. At the end of the episode, they end up trying to out-act each other in a play, taking a simple kiss scene and getting arrested for public indecencynote they were still just acting though. As they cheerfully compliment each other's acting skills, Haley tells her mother "I told you they just needed to fuck."
On Curious George it's pretty obvious there's something going on between The Man With The Yellow Hat and Dr. Wiseman, but sadly they're in a children's educational cartoon so they can't act upon their feelings.
The Legend of Korra is creating bucket loads of tension around a Love Dodecahedron of almost every possible pairing. First there was Mako-Korra. Then Mako-Asami. Then Bolin-Korra.
It should be noted that most of the tension exists between eventual Official Couple Korra and Mako, however.
However, after Korra and Mako break up for good in Book Two, the tension fades out in the background, and the two agree that they are Better as Friends. Since Book Three, the tension is now between Korra and Asami, who develop a very close friendship over the course of the next two books. The Grand Finale resolves it as much as Nickelodeon's S&P will allow, confirming that yes, Korra and Asami are the final Official Couple.
In The Legend of Zelda (1989) Link is constantly trying to get Zelda to kiss him. Sometimes she seems open to this, but something always happens to stop Link from getting what he wants, and he never kisses Zelda during the series. In the episode "The Missing Link" Zelda is only able to see Link's disembodied spirit because she is in love with him, though she refuses to admit it.
The Spectacular Spider-Man: In Episode 7, Peter takes Mary Jane Watson to the dance, and the two are clearly attracted to each other. In the next episode, she tells him they're "just friends"; however, hints remain throughout the show of a lingering attraction between them, Peter calling her "gorgeous" in his head in Season 2 for example. Since the show was cancelled after its second season, this tension was never resolved. However, since Peter and MJ are the main couple in the comics, its highly likely that they would have ended up together.
Transformers: Animated: Most of Optimus Prime and Elita-1's interactions (including their first scene together) imply they have feelings for each other, despite Elita dating Sentinel at the time. These feelings would also explain why she holds Optimus more accountable for her getting stranded on Archa Seven and eventually becoming Blackarachnia, despite it being Elita and Sentiniel's idea to go there in the first place. Even in the present day, the sexual tension between Blackarachnia and Optimus is very blatant in opposition to their conflicting alignments.
The Adventures of Jimmy Neutron, Boy Genius has the titular character and his rival, Cindy Vortex. Originally, it started off as Belligerent Sexual Tension, however as time went on and Jimmy and Cindy became closer friends, the belligerence all but faded out. The final episode has them openly flirting (they were playing footsie at one point), which results in The Big Damn Kiss at the end.
Mrs. Brisby and Justin from The Secret of NIMH they are clearly attracted to each other and Justin makes it his duty to protect her from danger, at the end of the film they go their separate ways after they succeed in their mission to move her house.
Harley Quinn (2019): Harley and Ivy spend half of Season 2 conflicted by their feelings for each other. Harley realizes she wants Ivy, but Ivy is already engaged to Kite Man and doesn't trust Harley won't break her heart if they start a relationship. After Ivy's wedding to Kite Man is ruined and Harley once again shows her she's working on being a better person, they get together.
