Korean dramas like to feature those three guys, usually with names and a generic personality frameset: the gossipy one, the play-by-the-rules one, and the Butt-Monkey.
Ant and Dec in everything they've ever been in, from their screen debut as PJ and Duncan in Grange Hill to their children's TV presenter gig to I'm A Celebrity, Get Me Out Of Here! They even appeared together on Desert Island Discs, which the BBC has never let anyone else do before or since. If you see them on TV, Ant is always the one on the left. Always.
Game show host Geoff Edwards had a tendency to do this on the shows he hosted- the other slot would be filled by an announcer or other crew member:
Him and the security guard, Emile Autori from The New Treasure Hunt, though it was nearly all one-sided on Geoff's part;
Him and the stage manager/off screen judge, "Erik von Judge" (real name Erik Warner) from Play The Percentages, who Geoff would frequently snark about;
Him and announcer Kevin McMahon from Starcade; the two would frequently tease each other (like Kevin claiming that he was gonna beat Geoff's high score on Sinistar);
And finally, him and announcer Rod Charleboi on The New Chain Reaction; this pairing was actually required by law. To elaborate, that version was taped in Canada and rules required Canadian content, so Rod was given an on-camera role to meet the quota.
Subverted in 30 Rock, with Grizz and Dotcom being anything but ordinary. They are, however, as close as "those two guys" can be for a man like Tracy.
Agents of S.H.I.E.L.D. has Leo Fitz and Jemma Simmons, with a rare canon portmanteau name of "FitzSimmons". And they're those two lab techs, which counts as its own trope by now.
Simmons has had two episodes about her "solo adventures" so far, and this trope doesn't apply so well anymore.
'Allo 'Allo!: Cairstairs and Fairfax are those two British airmen in the same uniform, both are brunettes and both sport a moustache. They always wear the same generic outfit as a part of their escape plan. They share a Catchphrase: "Hello!" "Hello!" They are practically indistinguishable.
In the Season 2 finale, Vir and Lennier are shown discussing their respective bosses' antics, secret agendas, clandestine meetings and unexpected character changes and commiserating over them and it is implied it is a weekly ritual.
We get two maintenance workers in a Season 5 episode with no clue what is going on as the station comes under attack by an unknown alien race.
There's Franklin and Marcus who are pretty important to the story, but still fulfilling a secondary story function to the main characters and sometimes comment on the events of the main story.
Marcus and Ivanova occasionally veer into this territory, although their characters are very distinct, and Marcus's feelings for Ivanova complicate things.
Battlestar Galactica (2003): Dualla and Gaeta are occasionally shown talking about what is going on, but by the last two seasons that role has been taken up by Racetrack and Skulls, who frequently fly vital and extremely hazardous Raptor scouting missions without any idea what the overall mission objective is, and complain about it.
Often in Blake's 7 a pair of Federation soldiers or technicians would be shown discussing the local situation. This would provide a human (though not always humane) face to the Gas Mask Mooks which were the usual face of the Federation.
Jesse's stoner pals Badger and Skinny Pete have been described as the "Rosencrantz and Guildenstern" of Breaking Bad, which is pretty fitting for a show often likened to the work of Shakespeare. Interestingly, they only become this trope from Season 3 onwards, after the death of their other friend Combo.
Jeffrey and Lester. These two may also be considered a Beta Couple to Heterosexual Life-Partners Chuck and Morgan. They have a rock duo called Jeffster, which is (unsurprisingly) terrible, or terribly awesome. Also, while they can be Those Two Guys in some episodes, they have some more in-depth treatment. First of all, they aren't indistinguishable from each other. Second, they aren't clueless about the show's Masquerade: it's revealed near the end of Season 2 that they know more about the Power Trio than anyone else, although they have still guessed wrong in a big way.
One-off characters Matty and Scotty have many elements of Those Two Guys. They're two stereotypical mobsters who have almost identical personalities. One is somewhat heavier in build than the other, but otherwise unless you're paying attention it's hard to tell which is which. They are more central to the plot than is typical for this trope, but don't actually do all that much themselves and spend most of their on-camera time tagging along injecting Plucky Comic Relief, and Leaning on the Fourth Wall about Chuck and Sarah's relationship. Many viewers and critics expressed disappointment when they were unceremoniously killed off at the end by the episode's Big Bad.
Chad and Roy, a pair of SWAT guys assigned to protect Chief Johnson after she got shot at in The Closer. They appeared in only one episode but they were really funny.
Whichever two lab rats happen to feature in any particular episode of CSI (particularly Archie or Mandy)... their personalities are just, y'know, those two lab techs. Yet they've almost all been around, just conversing in the background for the majority of the show. Every dozen or so episodes they get thrown a bone and have an actual episode featuring them. So much so that Hodges and Wendy have been upgraded to main cast members.
It always seems to have a pair that last a few years, which usually means they'll be nerdy and/or wannabe players.
JT and Toby were it for Seasons 1-6 until JT was killed, then Danny and Derek for Seasons 6-7 until Danny outgrew Derek and matured, and now recently Connor and Wesley have settled into Degrassi's Those Two Guys mantle, which had people shuffling in and out of that spot since Season 8.
Doctor Who has an interesting relationship with this trope.
Writer Robert Holmes was fond of having two minor characters in his serials whose main purpose was hanging around in the background being funny and commenting on the story, to the point that Whovians refer to Those Two Guys as the "Holmesian Double Act". When writers in the Whoniverse create characters like this, it's always done in reference to Holmes particularly in Eric Saward and Steven Moffat scripts.
The iconic "double act" are Jago and Litefoot from "The Talons of Weng-Chiang". Jago owns the theatre where Weng-Chiang is hidden and his agent plies his trade, and Litefoot is a police pathologist and the Doctor's de facto landlord for the story. Both important to the plot to the point that they are more important than the Doctor until the finale. In fact, Jago and Litefoot were so popular they eventually got their own series.
Pyp and Grenn. Pyp is a steward in the Nights Watch, Grenn is a ranger in the Nights Watch, they joined and trained at the same time as Jon Snow, and are close friends with Jon and Sam. Dolorus Edd is added into the mix in Season 2, as a brother of the Nights Watch who is close to this group.
Viserion and Rhaegal are rarely seen apart and given very little in the way of focus, contrasting with Drogon.
It has an extended version with Blair's entourage: an Asian-American nerd, a (possibly Hispanic for some extent) Queen Bee wannabe, an African-American beautiful girl an... well, the other one. For season three, it's done with Jenny's courtship.
Isabel and Kati, particularly in the first season.
Hiro and Ando were this in season 1 whenever Hiro wasn't contributing to the plot.
Season 2 had the twins Maya and Alejandro until the latter was killed by Sylar.
Horatio Hornblower has sailors Styles and Matthews gradually transform into this. In the first series, they play a part in Horatio's Character Development while he's a midshipman and new lieutenant, learning how to command; Matthews in particular is an experienced sailor who respectfully gives the boy some much-needed guidance. In the second series they're the only returning belowdcks charactersnote the other sailors in Horatio's division presumably still on the Indy but still provide a window into the discipline problems with the crew. In the third series they don't have much plot significance at all, apart from Styles doing time as the Surly Seaman of the Week.
Kaamelott: Many an episode is devoted to one of the usual duos pushing back the frontiers of human stupidity. Pretty much every character has been one of Those Two Guys in a three-person conversation, with the result of driving the third character (usually Arthur) up the wall, but several pairs stand out:
Perceval and Karadoc are forever finding new and stupid "martial arts" and trying to explain it to someone, or complaining about something to Arthur at three in the morning.
Yvain and Gauvain (Arthur's brother-in-law and nephew) are essentially Dumbass Teenage Sons in their twenties, who cannot be convinced to leave their fantasy world and be competent for a change.
Leodagan and his wife Seli are both greedy, cynical, powermongering jerks trapped in Awful Wedded Life. But woe betide anyone who disagrees with them because they are ruthlessly effective at comeback (given all the practice they have with each other).
Roparzh and Guethenoc are a pair of rival peasants unique in that they spend more time trying to kill each other than leading peasant revolts, both of which end up destroying the kingdom's food stores.
Mort Tubor and Bob Phillips in Knots Landing from Seasons Ten to Twelve. After Bob is Put on a Bus, Mort is on his own in Seasons Thirteen and Fourteen.
Lost had Steve and Scott until one of them died (no-one can remember which). They very rarely appeared and rarely had few lines.
Charlie and Hurley in the first two seasons or so, whose stories were largely separate from the core mysteries of the show and would sometimes be shown asking, "What's going on?" to the main characters and commenting sarcastically on, "There goes Jack and Kate off into the jungle again, up to who knows what?"
A retconned example would be Nikki and Paolo, who were apparently there all along observing events until they got involved in the main story and promptly died in the third season (due to fan dissatisfaction with these characters showing up from nowhere and them being expected to give a damn).
Mad Men has Ken Cosgrove, Harry Crane and Paul Kinsey as Those Three Guys for Series One.
Bulk and Skull, the school bullies in Mighty Morphin' Power Rangers. Unlike most sets of Those Two Guys, they remained constant characters in every season of the continuous plotline, cameoed in the first season after the continuous plotline, and even cameoed in the 10th anniversary Reunion Show.
Lothor's nieces Marah and Kapri on Power Rangers Ninja Storm also qualify, despite being part of the bad guys' crew instead of in the Rangers' social circle. (Cassidy and Marah are even played by the same actress).
Bulk himself returns in Power Rangers Samurai in this role for the first time in more than a decade, though Skull's son takes his father's place in the onscreen duo. This role gives Bulk the most appearances of any character in the series with nine seasons (As a regular in the six Zordon Era seasons, with a couple appearances in Power Rangers Lost Galaxy, a cameo in Power Rangers Wild Force, and as a regular again in Samurai), having formerly been tied with his friend Skull and Tommy Oliver.Though Skull appeared in the finale of Samurai, making him tied with Bulk.
Primeval has Tom and Duncan; Conner's geeky college friends who aren't in on the secret. Tom later contracts The Virus from a dodo and dies, and when Duncan finally reappears again in season 4, he has become a paranoid and reclusive Conspiracy Theorist.
An interesting take on the idea is in HBO's Rome, where Lucius Vorenus and Titus Pullo may be two of the main characters, but they are also playing a Rosencrantz-and-Guildenstern role where their stories, although important to them, are but a minor side-show compared to the unfolding civil war between Caesar and Pompey, which they observe and sometimes affect. This angle is lost in the second season, when their stories are largely separated from the bigger, more important characters, at least until the finale when they side with their patrons (Mark Antony and Octavian, respectively) once again.
Taken: Howard Bowen and Marty Erickson, Owen Crawford's two closest lackeys, in "Beyond the Sky", "Jacob and Jesse" and "High Hopes". After Crawford murders Bowen, Erickson appears in the next two episodes, "Acid Tests" and "Maintenance", on his own.
Brian and Kurt from the British TV series Teachers fit this trope almost exactly. Brian is the tall jock P.E teacher and Kurt is the short IT teacher. They could also be labeled as Heterosexual Life-Partners.
Veep made an unlikely friendship out of caustic asshole Jonah Ryan and poor, sweet Richard Splett. The two have nothing in common besides being idiots.
Weird Science: Matthew and Roger, seemingly the only friends that Gary and Wyatt have except for each other and Lisa.
The West Wing's Ed and Larry. Or Larry and Ed. They're in every meeting, advise the President on every issue and no one knows who the hell they are. Lampshaded a couple of times when they are given the wrong folders, and when someone asks if they always walk around together, or the time when the pair are introduced to a new character and when they ask "which one is Ed and which is Larry?", Ed, Larry and Josh all respond "it doesn't matter".