Rachel: You were our Fred and Ethel Mertz! Katie: Funny, I thought you were our Fred and Ethel Mertz.
— The Story Of Us
The Beta Couple is present in the backdrop of many Romantic Comedies and Dramas with The Hero of the story looking at wooing their Love Interest, to provide a Foil to his/her efforts you will see one of their closest friends have a remarkably easier time getting together. This "simpler" pairing is the Beta Couple.
The Beta Couple is always a secondary pairing (and foil) to the primary relationship. Often they are friends or confidants of one or both of them, it's not uncommon for The Hero and his wingman to simultaneously try to hook up with the heroine and her maid of honor.
Usually, they serve as a barometer for how well or poorly the main (alpha) couple is doing and offer possible solutions to any problems. Hit a Poor Communication Kills? The Beta Couple had that, but worked it out. Caught cheating? Losing "the spark" for your Love Interest? The Beta Couple had that, and here's how they got through it. In addition to all of that, if there is sexual tension that the Official Couple is oblivious about, the Beta Couple is all the more aware of it and will try to help them embrace it.
For these reasons, things tend to go more smoothly for them, letting them work as catalysts for the alpha couple's romance. That said, the Beta Couple is usually a source of comedy, and as such have more freedom to be unconventional and kinky and less problem (or at least conflict) prone than the alpha couple.
While the Beta Couple usually consists of secondary characters, sometimes the author(s) will decide that the main character has enough crap to deal with, make his relationship the Beta Couple, and make the bulk of the romantic conflict in the story concern the sidekick's relationship.
Compare Token Romance. See also Hooked Up Afterwards. Totally not related to Beta Test Baddie, but sometimes related to Pair the Spares or Romantic False Lead. Compare Alone Among the Couples, another foil to the main character's romantic life.
Has absolutely nothing to do with The Alpha Couple, surprisingly.
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Anime & Manga
Surprisingly, Agito and Yayoi from Air Gear, who by the half-way mark of the series had already reached a level of intimacy that took the main couple thirty-five volumes of story to reach.
Lots of couples in Eureka Seven. Namely Holland x Talho, Ray x Charles, Sakuya x Norb. Dominic x Anemone is probably the most popular.
Subverted by Dominic x Anemone. They face loads of troubles in their relationship throughout the series (mostly for Dominic, who spends almost the entire anime trying to get Anemone to notice him), and thus their relationship is more of a parallel to the main pair than a mere Beta Couple. The same may also be said for Holland x Talho. A true Beta Couple from the series would be Moondoggie x Gidget or, as suggested above, Norb x Sakuya.
Though there are several couples in Clover the only seemingly happy pairing in which both members are still alive at the present time are the Yaoi Guys Gingetsu and Ran and even they are probably doomed in about five years.
And also to an extent in the anime: the scene where both Akane and Mai use their CHILDS makes it clear they are very similar. Akane is then defeated by someone she thought was a friend (Miyu), resulting in Kazuya's demise. Same thing happens to Mai (she gets attacked by Shiho, with whom she was friends before Shiho found out she was a contender for Yuuichi's heart, then Shiho's child gets destroyed by a brainwashed Mikoto, killing Yuuichi).
Code Geass - Suzaku and Euphemia could be this… if there was an alpha to begin with. The typical beta couple is the couple involving the most important people after the couple involving the protagonist. But here, the protagonist is a Celibate Hero, so Suzaku and Euphemia were the only couple displayed in some openings.
Ougi and Villetta, kind of beta for Suzaku/Euphie, but actually the only couple which ends well (not that Suzaku stopped loving Euphie: she dies).
Natsumi and Kotaro. As of chapter 262, they definitely count as canon. Kiss, pactio, etc. Wow. As of the conclusion of the manga, in contrast with the couples mentioned above, Natsumi/Kotaro are set in stone, given that they get married in the epilogue.
Princess Amelia of Slayers definitely has feelings for Zelgadis but, due to his quest to recover his human body and being the only serious guy of the group, for the most part he doesn't remark on it or doesn't care. However, she does make him blush a lot, and there are many hints that he cares for her quite deeply, especially in the second season.
And the fact that we see that one of Amelia's wristbands is tied to Zel's canteen in the credits of the last episode of the third season.
Neon Genesis Evangelion - Aside from the primary Love Triangle of sorts between Shinji, Rei and Asuka, we have both Kaji/Misato and Touji/Hikari. This being Evangelion, neither fares particularly well, at least not for long...
Tsubasa Reservoir Chronicle has somewhat of an inversion. The main protagonists Sakura and Syaoran were actually the ones with the more simplified relationship as opposed to the ambiguously canon Beta Couple Fai and Kurogane, possibly attributed to the fact that Sakura and Syaoran were carry-overs from the already canon version of themselves in Cardcaptor Sakura, so there was no question that they'd get together. Whereas Fai and Kurogane were entirely new characters who got their Character Development over the course of Tsubasa. Even so, they still frequently acted as parental figures to Sakura and Syaoran, as well as parallels/foils to them in various official artwork and in-story plots and jokes, such as their Outo Country names: Big Dog (Kurogane), Little Dog (Syaoran), Big Cat (Fai) and Little Cat (Sakura).
Orie and Hinako from Aoi Hana, who Fumi sees as having the ideal happy lesbian relationship.
In Bakuman。, Akito Takagi and Kaya Miyoshi are the Beta Couple. Their down-to-earth approach to love and marriage and their frequent bickering is a nice contrast to the romantic idealism of the Alpha Couple, Moritaka Mashiro and Miho Azuki. The contrast between the two couples is not lost on any of the people involved, as Mashiro wonders if he and Azuki should be more like Takagi and Miyoshi (who have gotten married despite confessing their feelings later than Mashiro and Azuki), before resolving to keep his promise.
Tenshi Ni Narumon: Raphael and Mikael are somewhat an inverted Ho Yay Beta Couple to Noelle and Yuusuke as it's implied that they have been in a relationship long before the series actually started and their relationship is...a lot less innocent that Noelle and Yuusuke's.
Yuuji and Shouko in Baka to Test to Shoukanjuu, though their relationship isn't all that different from the main's, lack of a Love Triangle aside. Voyeur and Aiko are probably a more "normal" example.
Hyper Police uses this trope later on in the series when Tommy and Poe hook up. Tommy is already Banten's wingman, and Poe takes Natsuki under her wing (And her slippers, yeouch!) to try and save her relationship.
It's kinda... complicated in Yandere Kanojo, since the supposed first couple (Reina and Manabu) is went out without hitch. The secondary couple (Hijiri and Shiratori) is the one who shown the growth. There are another, less significant Beta Couple, like Reina's parents, and The Principal and his wife.
Tonari no Kashiwagi-san has Sayaka and Kazuki who often help Kotone and Yuuto along with their stumbling more-than-friends-but-not-quite-going-out relationship, both through direct advice and as a Double Date couple to keep the two from being too nervous, although mostly Yuuto, as Kotone is even more innocent than that.
Post-issue #50 in Archie Comics' Sonic the Hedgehog series, Antoine D'Coolette and Bunnie Rabbot became the beta couple to Sonic the Hedgehog and Princess Sally Acorn.
Druid City features the main character's homosexual brother, Mike, in an Opposites Attract relationship with Pet Homosexual Dusty Crocker. While they have their own problems, Mike and Dusty's relationship spans the entirety of the series and serves as a contrast to the far more tumultuous relationships that the main character, Hunter Hastings and female lead Becky Fink, engage in separately.
Taniguchi and Yanagimoto in Kyon Big Damn Hero have officially stated that Taniguchi is trying to paint themselves as the Beta Couple to Kyon and whichever girl he's being shipped with. There's Haruhi, Mikuru, Yuki, Kanae, Tsuruya so far...
Sirius and Aletha in the Dangerverse—quite literally, since they live in a "Pack" and are considered the Beta male and female.
In a lot of Naruto fanfiction that puts Naruto and Hinata in the spotlight, Sasuke and Sakura are usually the Beta Couple. The inverse is also possible - for example, in White Rain, Sasuke and Sakura are the main pairing, with Naruto and Hinata as the Beta Couple.
For those who don't particularly like Sasuke and Sakura, there are a lot of other pairings that can step up to the plate.
Most fanfics of Puella Magi Madoka Magica center on either Madoka/Homura or Kyouko/Sayaka. The one that isn't the main focus will usually be the Beta Couple to the one that is.
Alpha and Omega has Garth and Lilly, who were spending time together while the Western pack desperately searches for Kate before a pack war starts. While Kate and Humphrey, who were darted and trucked to Idaho and struggling to get back to Jasper, falling in love along the way, Garth and Lilly find themselves hitting it off beautifully. In fact, it gets to the point where the Western pack Alpha prince would be more than happy having Lilly substitute for Kate, even though Lilly is an Omega.
John and Mary in WALL•E play this role to the titular robot and Eve. The parallelism between them helps reinforce the theme: Wall-E and Eve are robots, whereas John and Mary are humans whose upbringing in an impersonal consumerist dystopia has robbed them of their humanity. In both cases, they (re)discover their humanity partly through connecting with one another.
Though all the couples in Toy Story are on equal standing, Buzz and Jessie are this to Woody and Bo Peep, pairing up at the end of the second movie. And we cannot forget Mr Potato Head and Mrs Potato Head.
They were this to Woody and Bo Peep before the couple got tragically split for good between Toy Story 2 and Toy Story 3, anyway.
Films — Live Action
Albert is the dating challenged man that "date doctor" Hitch is trying to help get together with celebrity Allegra Cole. Despite his nervousness things go smoothly for them. While Albert and Allegra's relationship continues to progress, Hitch finds that none of his tried and tested methods are working for him, despite being a master of the art.
Wedding Crashers has Jeremy and Gloria, a mentally unstable nymphomaniac. Despite torturing Jeremy with/during sex, and being desperately possessive and scary, the two end up getting together while John and Claire hit a rough patch. The irony here is that John forced Jerry to date Gloria so he would have shot with Claire, only for it not to pan out at first. It's even more ironic (and plays the trope straight) considering John and Claire didn't hook up until they were forced to be in the same room with each other during Jerry and Gloria's wedding as the best man and maid of honor.
Lucas Belvaux has made a trilogy of movies (a comedy, drama and thriller) re-telling the same few days from three perspectives. Each of the three couples was the alpha couple in one of them and a beta couple in the two others.
A Kind of Loving begins with the wedding of Christine and David, and they provide a tranquil counterpoint to the stormy relationship of Vic and Ingrid throughout.
The 1998 made-for-television film Merlin has Frik and Morgan le Fay, whose romance ends a lot less happily than Merlin and Nimue's.
Most Porn with Plot movies will slightly parody this or take it to its "area". The routine is of a normal suburban couple which needs its love life spiced up by the couple that "has seen it all and knows it all". Of course, it tends to become an Undead Horse Trope because of all its use, so sometimes it's parodied, subverted, played with (the couple is of lesbians, or it's just one woman teaching everything etc.) and whatnot.
Enchanted's Nancy might lose her fiancée Robert to Naïve Everygirl Giselle, but at the end of the movie she marries Giselle's ex boyfriend Prince Edward.
Jacques and Lulu in the movie musical The Love Parade provide a plebeian contrast to the royal principal couple.
In Monsoon Wedding, the romance between the day labourer and the maid Alice progresses faster than the one between the husband and wife despite the fact that those two are the ones actually getting married.
Going the Distance has two, Erin's sister and her husband, who provide more traditional relationship advice, and Garrett's co-worker and her boyfriend (mentioned, but never seen), who provide more long-distance related advice.
Pete and Debbie to Official Couple Ben and Alison in Knocked Up. In this case, the Beta Couple mirrors the Alpha couple's dynamic but turned Up to Eleven to the point where it's nearly inverted. Alison is a smart, driven, competent career woman and much of Ben's (a lazy stoner) arc is learning to take responsibility and become worthy of her. By contrast, Pete is more relaxed and laid-back than Debbie, but not to the point of being lazy or irresponsible, and Debbie is neurotic and controlling and her arc is about learning to relax and love Pete for himself instead of trying to "fix" him.
Jane Bennet and Mr. Bingley to Elizabeth and Mr. Darcy in Pride and Prejudice; the Official Couple (the girl who falls for a charismatic The Casanova before discovering his true colors before growing to esteem and appreciate a worthy man) and Beta Couple (the man forbidden from proposing to the girl he loves because his family doesn't believe she is rich enough) are essentially reversed from Sense and Sensibility. Jane and Bingley are a humorous example because they're only the Beta Couple to the reader. Since Elizabeth is the protagonist, she and Darcy of course form the Alpha Couple of the story. However, in the world of the story itself, it's Elizabeth and Darcy who are the Beta Couple, since pretty much from the get-go, the people around them are waiting to see if Jane and Bingley will hook up.
Sparhawk and Kalten in David Eddings's Elenium and Tamuli series. Sparhawk marries Queen Ehlana and Kalten falls for her personal maid Alean. Also Melidere and Stragen, and Talen and Danae, and Sephrenia and Vanion.
It's taken to an extreme in the Belgariad/Malloreon: Hettar and Adara, Silk and Velvet, Durnik and Polgara, Mandorallen and Nerina, Lelldorin and Ariana, 'Zakath and Cyradis, Relg and Taiba, Beldin and Vella, a reunited Belgarath and Poledra... granted, for those who love happy-ever-after cliches, Eddings is made to order.
It's a smooth and quick hook-up for Roger and Bonnie in Jennifer Crusie's romance novel Bet Me, compared to the more rocky relationship of their respective friends Cal and Min.
Conaire and Caitlin are a classic Beta Couple in Jules Watson's The White Mare. He's the hero's right-hand man and she's the heroine's best friend, and their relationship is far less complicated than that of the main couple.
Spook and Beldre in Mistborn, though Spook was originally a Mauve Shirt that got promoted to main character in the third book.
The duchesse de Nevers and Coconnas fill the spot in La Reine Margot, but they are less peaceful than Margot and La Môle.
The Hunger Games has Finnick and Annie. While Katniss and Peeta/Gale are never really sure where they stand, Finnick and Annie are deeply in love, with Katniss envying their certainty. Finnick helps Katniss deal with her worry over Peeta, and in the end, Finnick's death means they take the Star-Crossed Lovers title well away from Katniss and Peeta.
The Flight Engineer has Chief Petty Officer Paddy Casey and Second Lieutenant Cynthia Robbins. The fact that their relationship is against regulations prompts Casey to try and get into officer candidate school.
Simona Ahrnstedt follows this pattern in her debut novel Överenskommelser. We have Beatrice and Seth, the troubled alpha couple, who need a painful twenty months to sort things out, contrasted by Sofia and Johan, the much happier beta couple. But the story also introduces us to another beta couple, Jacques and Vivienne, who need as much time to sort things out as the alphas do.
In Song of the Lioness Eleni Cooper and Baron Myles quickly fall for each other while Alanna is sorting out what kind of romance she even wants with Jon, George, and Liam. Jon and Thayet play like this as well (despite him being king) since they pretty much fall in love at first sight.
Raoul and Buri start dating and soon become engaged in Protector of the Small's third book. Kel is busy dealing with her crush on Dom and wondering how far her relationship with Cleon will go given their situations. Neal and Yuki also seem to have a pretty easy relationship.
In Provost's Dog Ersken and Kora, a Dog and a criminal who seem to have no trouble dealing with the Dating Catwoman situation. Meanwhile Beka and Rosto have copious amounts of UST thanks to her unwillingness to bed a criminal.
Circle of Magic: Lark and Rosethorn are in a happy, stable, and open relationship. Although this isn't made explicit until the Circle Reforged books, those are the only books in which the protagonists start exploring romance anyway, usually with a lot of fumbling.
The Charlie Parker Series has Angel and Louis, who are generally content in their relationship (if not in other aspects of their lives), act as the beta couple to Parker and Rachel. however, later books reveal that there's something slightly sinister behind Angel and Louis's relationship... Also, once Parker and Rachel split up, the emphasis on Angel and Louis' relationship briefly increases, then falls away almost completely, as does their presence in the books. Between The Reapers and The Wolf in Winter, their cursory appearances always have them ask after Parker's current love interest, and their very settled relationship provides a nice contrast with Parker's slightly more turbulent lovelife.
Live Action TV
On The Nanny, Niles and CC play this role after they were hooked up together. They were quite a fun Beta Couple since they hated each-other as much as they were in love, so they were always attacking the other.
Turk and Carla in Scrubs. At multiple times J.D. has mentioned that they act as a unit giving advice to others, to the point in one fantasy based episode they were portrayed as a two-headed witch.
One could argue that Turk is in both the Alpha AND Beta Couple, if you consider the Alpha Couple to be Turk and JD.
Friends: Monica and Chandler become this to main couple Ross and Rachel in the later seasons. However they vary from the classic Beta couple mould as a lot of screen time is given to their developing relationship and they certainly face problems. (Rather than having it 'all figured out' from the beginning). The difference is they learn to deal with their issues while Ross and Rachel bicker and fight. Ironically this means you see more of their relationship (spanning over half the series) than Ross and Rachel who were only together for about a season.
Buffy the Vampire Slayer: At various times Willow and Xander would be in a relationship to contrast Buffy's various relationships. Willow/Oz and Xander/Cordelia in the earlier seasons, then Willow/Tara and Xander/Anya in the later seasons (and Willow/Kennedy in the last).
On Angel this was modified with a Love Triangle for the Beta Couple between Gunn, Fred and Wesley, while Angel began a relationship with Cordelia.
To be specific, Gunn and Fred were the Beta Couple on their own during seasons 3 and 4. While Angel and Cordy were trying to figure out that they were in love with each other in the third season and god knows what happened to Cordy in the fourth, Gunn and Fred had a fairly stable relationship from the time they got together until "Supersymmetry".
Except for Josh/Donna and CJ/Danny of course, who were upgraded to Official Couple and ended up together in the final season.
Stanley and Mimi in Jericho. Oddly enough however, their pairing became the only major romance of focus throughout most of season one and all of season two pummeling the hell out of the pretty much forgotten (by the writers) Heather/Jake/Emily triangle, which from a story-telling standpoint, should've been the romance arc of focus.
Helo and Athena in Battlestar Galactica, especially considering they are one of the only couples that remain steady throughout the series.
How I Met Your Mother has Marshall and Lily, getting engaged in the pilot episode and having been together for some 8 years prior. Besides a temporary break-up in the early second season they act as a unit and are seen by Ted as the perfect couple that he wants to model himself after. What is interesting is there is a distinct lack of an Alpha Couple or at least a rotating Alpha Couple with Ted and whoever he is dating, such as Robin for the entire second season. Barney/Robin also has the trappings of an alpha couple because of how chaotic their relationship was, but they get married before even Ted does. In the end, the ultimate Alpha Couple will be Ted and "the mother."
For the first two seasons of The O.C., Seth and Summer were the Beta Couple to the Official Couple of Ryan and Marissa. In the third season, Ryan and Marissa break up for good and there is no real Official Couple. In the fourth and final season both Seth/Summer and Ryan/Taylor are given about equal weight.
Arthur and Morgana have a Will They or Won't They? that mirrors Merlin and Gwen's in the first Series of Merlin. But in Series 3, Arthur and Morgana are revealed to be brother and sister, so it's pretty unlikely to become canon! It should be noted, however, that it hasn't stopped the shippers. In fact, you could argue that almost every potential Beta-pairing (including Gwen/Lancelot, Merlin/Morgana, and particularly Arthur/Merlin) is more popular among fans than the Arthur/Gwen coupling.
D'Argo and Chiana in Farscape, though theirs is a tempestuous, mostly physical relationship that's more off than on, and is ultimately doomed. Nevertheless, both Chiana and D'Argo often dispense relationship advice to Crichton and Aeryn. A (marginally) less dysfunctional example is the tragically brief relationship between Stark and Zhaan.
Smithy and Nessa in Gavin and Stacey. However, in later seasons Gavin and Stacey's relationship stabilises considerably, while Smithy and Nessa's provides most of the drama, essentially making the eponymous Gavin and Stacey the Beta Couple.
Firefly has Zoe and Wash, a happy married couple, as the Beta Couple to Mal/Inara and Simon/Kaylee,(Gamma couple?), though neither Mal/Inara nor Simon/Kaylee are actually a couple throughout the series.
Angela/Hodgins to Booth/Brennan. Angela/Hodgins are in many ways the LESS stable couple. "The Witch in the Wardrobe" sounded somewhat surprising (but much-loved) wedding bells for Angela and Hodgins, after several episodes of rekindled feelings. As of the fifth season finale, they're on honeymoon in Paris.
Will and Djaq from the 2006 series of Robin Hood. Their relationship ends up being much more successful than Robin and Marian's.
In Mad About You, Fran and Mark (although in a "what not to do" sense), and later in the series, Debbie and Joan. Or alternatively, one could consider Paul and Jamie to be the Beta Couple to those guys, as they were more stable than Fran and Mark, and they were together for longer than Debbie and Joan.
In Skins, despite its numerous couples in every generation, only Grace/Rich in Generation 3 truly fit this trope, as they've had relatively smooth sailing compared to every other possible coupling in their cast. In the previous generations, both intended Beta Couples (Sid/Cassie and Naomi/Emily) proved to be far more popular than their generations' Alpha Couples (Tony/Michelle and the Freddie/Effy/Cook Triangle of Doom), and thus were promoted to Alpha status in their second series, with the attendant Conflict Balls being thrown their way. And it wasn't like they were without conflict to begin with anyway.
In Venezuelan telenovela Cosita Rica (2003), although Diego Luján and Paula C were the alpha couple, their respectives siblings — Verónica and Cacique — being the beta couple, attracted a lot more attention than the alpha one, to the point the actress who played Paula C almost left the show because of this. In fact, the actors who played Verónica (Marisa Román and Cacique (Edgar Ramírez) became very famous. Ramírez even made his way into Hollywood, appearing alongside Keira Knightley in Domino and in Bourne Supremacy.
Victor and Sierra in Dollhouse are the beta couple to Paul and Echo. Subverted in that Paul and Echo never got beyond the UST phase, while Victor and Sierra ended up with a kid.
John Doggett and Monica Reyes on The X-Files could be considered the beta couple to Mulder and Scully's alpha, though their relationship and UST started mostly after Mulder and Scully were already an established couple. Unfortunately for fans of the ship, the show didn't run long enough with them as head investigators of the X-Files for their relationship to be fully established (though there was a good dose of shippiness in season 9); it is unclear what became of them after the series finale. They did not appear in The X-Files: I Want to Believe.
Curtis and Alisha during the first season of Misfits, despite also being the Official Couple and having a fair bit of relationship drama in their own right. Whether or not the show itself actually treats them as a beta couple is debatable, but the fandom indisputably saw Nathan and Kelly as the alpha couple, despite them not getting past the UST stage. Come the second season, things change entirely, with Alisha and Simon becoming the alpha couple (both in-universe and in the eyes of the fandom), and Nathan and Kelly's awkward almost-romance fizzling out as they decide to just be friends - although they're still a hugely popular pairing among fans, so whether this is really the end for them has yet to be seen.
In Gilmore Girls, Lorelai Gilmore's best friend Sookie has a much easier time finding a mate in Jackson than Lorelai has making it work with any of her boyfriends. Rory Gilmore's best friend Lane also has a much easier time making a permanent relationship than Rory does.
Alex and whomever she is dating, and Justin and whomever he is dating. True to form, Harper and Zeke (who got together at the end of season 2) have outlasted their best friends' more passionate but more fleeting relationships.
At one point, even Juliet and Mason were a Beta Couple, due to the fact they had been in a romantic relationship, before each one became Justin and Alex's girlfriend and boyfriend respectively.
Caroline and Matt were one to Stefan and Elena on The Vampire Diaries. Possibly subverted as it was always made pretty clear that Matt still had a thing for Elena. A more traditional Beta Couple would be Alaric and Jenna. Season 2 has two Beta Triangles to the main Stefan-Elena-Damon one: Tyler-Caroline-Matt and Jeremy-Bonnie-Luka.
Artie/Tina was this for the first season, compared to the Rachel/Finn/Quinn/Puck mess and Terri/Will/Emma. In the second season, after breaking up with Artie over the summer, Tina and new boyfriend Mike became this, compared to the Rachel/Finn/Quinn/Sam mess and Holly/Will/Emma/Carl. In the second half of the season, Puck/Lauren and later Kurt/Blaine have also assumed this role.
After Finn died, the remaining romances on the show were bumped up in importance: Kurt/Blaine became Glee's Official Couple with Brittany/Santana and Sam/Mercedes as the Betas.
Leverage has Hardison and Parker to Nate and Sophie. Hardison and Parker have minor problems, but mostly as a result of Parker being emotionally troubled.
Once Angela was added to Boy Meets World in season five, Shawn and Angela became this to Cory and Topanga, except when they break up during season six.
On Parks and Recreation, Andy and April have become this to Leslie and Ben, even giving the latter couple relationship advice on a few occasions.
Tristan and Isolde on Merlin serve as the catalyst for getting Arthur and Guinevere back together.
In Chinese Paladin, Tang Yu and Ah Nu are this, although they fulfil the "foil to the main couple" role only in being equally dysfunctional.
Toshiko and Owen to Gwen and Rhys in Torchwood. Jack and Ianto start out as the Beta Couple and become the official one in Season 3, replacing Gwen and Rhys.
In Carrusel Susana and Rene have a smooth and stable relationship...as compared to Valeria and David having so much drama!
Constable Crabtree and Dr Grace in Murdoch Mysteries (to Murdoch and Dr Ogden). He's a bright by-the-book police officer, she's a New Woman pathologist. He's sometimes shocked by her modernity, but usually finds she inspires him, she can get exasperated by some of his more old-fashioned values, but respects that he sticks to his principles. And yes, that's also a perfect description of William and Julia.
Much Ado About Nothing plays with the conventions. Initially, Claudio and Hero are the happy beta couple, and Beatrice and Benedick are the bickering alphas. The rest of the cast decides to trick B&B into admitting their love for each other, with amazingly quick success—by the midpoint of the play, everyone's soppy in love. Then Claudio is led by slander into accusing and abandoning Hero, and Benedick agreeing to challenge him on Beatrice's behalf. The play ends with both couples getting married. It's almost as if Shakespeare set out to write a sappy romance with Claudio and Hero as the Alphas but got so interested in the Beta Couple that they got promoted. (The opera version drops the whole Claudio and Hero story.)
Another good example of musical comedy's predilection for adding a Beta Couple for the sake of comic relief is The Most Happy Fella, whose Cleo and Herman have no counterparts in the non-musical source play.
In Sweeney Todd: The Demon Barber of Fleet Street, the two couples are Anthony and Johanna as well as Sweeney and Mrs. Lovett, but it's not straightforward which couple is which. Anthony and Johanna have the more conventional romantic arc, with Todd and Lovett helping them out, and Mrs. Lovett's courting of Todd being more in the way of comic relief. On the other hand, Sweeney Todd is the title character and lead role, and it's Mrs Lovett's doomed crush [[Yandere on him]] that brings about the tragedy of the play.
Many of the Rodgers and Hammerstein musicals include a Beta Couple:
In The King and I, Tuptim and Lun Tha are written like a Beta Couple, but Anna's relationship with the King of Siam is obviously not a romantic one. Both relationships end in tragedy.
State Fair has Abel and Melissa, though Blueboy manages to find love as well.
Nathan and Adelaide from Guys and Dolls are an odd case, as they are a Beta Couple in role alone; in stage time and importance they are equal to Sky and Sarah. It also should be noted that they were never paired in Damon Runyon's original stories.
Jimmy and Snookie from 110 in the Shade; less so in the original non-musical play it was based on, The Rainmaker, in which Snookie does not actually appear.
In StarKidPotter'sMe and My Dick, the main Beta couples are the alpha couple's body parts, Dick and Miss Cooter and Joey and Sally's hearts, and Joey and Sally can only get together when they are happily paired off. There are a couple less prominent beta couples too, like The Old Snatch and Big T.
In the Heights has two couples but both are given equal prominence. If one had to be picked it would be Nina and Benny behind Usnavi and Vanessa since Usnavi is clearly the main character.
Deconstructed mercilessly in Who's Afraid of Virginia Woolf?. At first, newlyweds Nick and Honey appear to be this to the severely dysfunctional marriage of George and Martha. By the end, however, it's become apparent that though George and Martha are indeed a dysfunctional couple, they also have a very strong bond holding them together. By contrast, Nick and Honey have dealt with problems by ignoring or hiding them, and are implied to be on the road to an even more miserable marriage.
Spring Awakening has both Moritz/Ilse and Hanschen/Ernst as the Beta Couples to Melchior/Wendla. Subverted in that both relationships are as twisted and messy as the main one: Moritz kills himself, and while Hanschen and Ernst end the story slightly better off, Word of God says they weren't going to end up well either.
A standard feature of any Usles pantomime - the main love interests usually have friends, advisors or servants who fall for each other. Sometimes this doesn't happen until the very end of the show, when it can also end up as a case of Pair the Spares.
Subverted in Of Thee I Sing. Jenkins and Miss Benson, respectively Wintergreen and Mary's secretaries, usually appear together but have no love plot of their own.
Bubble Symphony, aka Bubble BobbleII, introduces Cororon and Kululun, both who also get cursed with Bub and Bob and turn into bubble dragons. Coro and Kulu are magenta and orange respectively. They never appear in any other Bubble Bobble game.
Keep in mind that Bub and Bob are male, and Coro and Kulu are female.
And Pab and Peb(source) Title Operations Guide in Shop Channel, the new Beta Couple in Bubble Bobble Plus (WiiWare). They're still magenta and orange and both female.
Another subversion: Contra 4 for the DS not only brought back Bill and Lance, the original Contra duo, but also introduced a Beta Duo in the form of Mad Dog and Scorpion, whose names are Shout Outs to Bill's and Lance's former nicknames from the American localization of the NES games. While Bill and Lance wear blue and red (their colors from the NES games), Mad Dog and Scorpion wear green and purple, which were Bill's and Lance's colors in the arcade version of Super Contra.
Tali'Zorah vas Normandy and Garrus Vakarian at the end of Mass Effect 3, should you not romance either one of them. Especially prevalent if your romance is Liara. Joker and EDI also become an item after the latter gains a Fembot body.
Aveline and Donnic in Dragon Age II. Notable for requiring an extremely silly sidequest to bring about, and for the even sillier lines the whole thing draws from the rest of your team.
Varric: "Let me draw you a picture of where she wants you to touch her..."
Lulu and Wakka from Final Fantasy X, who have a bit more of a harder time getting together than Tidus and Yuna, who were pretty much in Love at First Sight. Though understandable, as Lulu had previously been with Wakka's brother (who had died). But interestingly enough, Lulu and Wakka get married and have a kid before Tidus and Yuna, seeing how Tidus was the fayth's dream and had to leave Yuna.
Tales of the Abyss has Natalia and Asch playing Beta to Tear and Luke. Note that this doesn't fit the idea of the Beta Couple as having a simpler or more easy-going relationship. At all.
Agarest Senki 2 has two of them. The first couple is Janus and Chloe in the first generation, and the second couple is Ignis and Cynthia in the second generation. Both couples then had a child each (Jude, and Lizerotte respectively).
In universe, though, Elliot and Sarah take this role, with Tedd and Grace serving as the main couple. Or Ellen and Nanase. Not sure where they fit.
Tedd/Grace and Ellen/Nanase are the alpha couples since a large part of the storyline revolves around their relationships. Elliot/Sarah is a definite Beta Couple though, and maybe Susan/Catalina, although they aren't a couple..
Casey and Mary in Casey and Andy. Subverted somewhat in that Andy Weir ditches the "one for romance" part of the idea and just plays both couples (Casey/Mary and Andy/Satan) for laughs.
Erika and Largo in MegaTokyo are a classic case of a Beta Couple used to provide a light, humorous contrast (most of the time) to the much more dark and dramatic main couple: Piro and Kimiko.
Melissa and Kurt from Multiplex. Outside of Kurt's habit of pulling pranks on Melissa, they're the rock of love compared to the Jason/Jay/Becky/Angie quagmire.
The Law of Purple subverts this trope in an odd way; there are two clearly defined couples amongst the main characters, which take turns being the Alpha and Beta couples depending on which pair contains the character(s) who are the focus of the current arc. At the time of this writing, Blue and Lette are the designated Beta Couple. And that's not even considering what the rest of the cast is up to...
Subverted in Questionable Content when alpha couple Faye and Marten doesn't happen and Beta interest and Alpha character end up forming a strange mix between Alpha and Beta couple — Dora and Marten.
Roy and Celia in The Order of the Stick, who manage to play the calm, laid-back beta couple to Haley and Elan's angst-ridden alpha despite the fact that Roy spends a large proportion of a plot-arc dead. The role is also played by Mauve Shirt couple Kazumi and Daigo, who are happily married (and expecting) already, despite having only gotten together after Haley and Elan got together.
In most Heterodyne stories, while Bill is canonically paired with Lucrezia, his brother Barry is paired with whoever the "High Priestess" character happens to be this time.
Mell and Caliban in Narbonic are a nice, steady evil couple who provide nice contrast to the main pairing of Dave and Helen.
Abbey and Daisy in Bittersweet Candy Bowl. This is in stark contrast to the angst, anger, heartbreak, confusion and jealousy experienced by the (many) other characters on an almost daily basis, though Abbey certainly has some personal issues.
Sunstone has the happily married Cassie and Tom make the various romantic heroes look like the shambles they are.
Code Lyoko: Jeremie and Aelita are the Beta Couple for the Yumi/Ulrich relationship and the William/Yumi/Ulrich/Sissi love square, and they in fact become an Official Couple while the love square never gets resolved.
Winx Club has at the end of season 1 two Beta Couples: Stella and Brandon, and Tecna and Timmy. By the end of season 2, Musa has hooked up with Riven, while Flora is dating Helia. At the end of season 3, there are five with Aisha and Nabu dating each other. All of the couples have gone through their rough spots and struggles, while Musa and Riven have almost as much conflict as Bloom and Sky, the main couple. At the end of season 4, there are only four due to Nabu's death.
Gerald and Phoebe from Hey Arnold!; heck, unlike Arnold and Helga this one isn't (mostly) one-sided.
Word of God mentioned that they would have been an explicit Beta Couple in The Patakis, had the series been green-lighted. They would've been the "cool couple" to contrast with the more complicated relationship of Helga and Arnold.
Stacy and Coltrane on Phineas and Ferb. Since both of them are rather laid-back, their romance is meant to be a contrast to Candace's neurotic attempts to get Jeremy's attention.
One could argue Ferb's pining for the older Vanessa is a Beta Couple for Phineas and Isabella.
Amy Wong and Kif Kroker from Futurama to Official Couple Fry and Leela. The latter go through a lot of Will They or Won't They? before finally settling down, while the former are mostly kept apart by circumstance (Kif being a military man who's often away on deployment).
Gunther and Jackie on Kick Buttowski, albeit only canon in one episode (despite Gunther calling her lovely and etc in later episodes) does serve as a beta couple for the much more popular Kick and Kendall relationship.
Often used as a beta couple in Kick ButtowskiFanfiction stories focusing on Kick and Kendall's relationship (which is most of them).
Super Robot Monkey Team Hyperforce Go! has an inversion. It's the main character who has a Beta Couple relationship with his Robot Girl girlfriend. While Chiro and Jinmay are shown with a solid and happy relationship since her introduction and she's usually absent, it's Sprx and Nova the ones who get more screen time and have the more dysfunctional dynamic, pretty much making them the Alpha Couple of the show.
Adventure Time's Jake the Dog has a fairly stable long-term relationship with Lady Rainicorn, contrasting Finn's difficult growing into puberty and dealing with unrequited crushes.