'Allo 'Allo!: Lieutenant Gruber. Word of God confirmed it during the recent reunion special, but the Where Are They Now epilogue leaves it ambiguous by showing that he married Helga after the war and had children with her.
Also, General von Flockenstuffen is said to be "a bit this-a-way and that-a-way."
The Amanda Show: Had Penelope, who wanted to be Amanda's "best friend" really badly. The website plays it even thicker with tons of captions over her affections for Amanda, her saying she doesn't find a male actor on the show attractive, and her all but outright drooling over cheerleaders. Getting Crap Past the Radar, maybe?
Are You Being Served?: Mr. Humphries. He was effeminate, camp, and often talked about his dubious 'leisurely activities', yet it was still hinted that he might actually be straight. John Inman, the actor who played him, came out of the closet years after the show aired.
Arrested Development: Tobias. The (often) very obvious homosexual undertones in his lines are possibly the show's longest running gag.
"I wouldn't mind kissing that man between the cheeks, so to speak."
As of Season Four, a lot of Gob's more eccentric relationship behaviors in the first three seasons retroactively became this.
In the same vein is Amy. While she is in a committed (if sexless) relationship with Sheldon, she has a tendency to make some odd comments about her "bestie" Penny and her beauty. And there was the time she got drunk and kissed her. And the time she wanted to have a bachelorette party that involved stripping naked and painting on each other. Also the time she said Penny had a better chance of getting with her than Leonard did. The list goes on. Of course a lot of it is simply social awkwardness and over expressing her joy at actually having friends, especially a friend with social graces like Penny (aka the resident Cool Big Sis). Amy is more Ambiguously Bi.
Gus Fring may also count, as his relationship with his former business partner Max Arciega was extremely close and he endowed a chemistry scholarship in Max's name years after his death. Word of God has said this is a valid interpretation of their relationship.
Buffy the Vampire Slayer: Andrew is the king of this trope. He all but said he was in love with Warren, and did as he said because "He promised we'd be..." (he does cut off uncomfortably at that point, so it seems likely he was closeted). He has rather clear moments of lust over Spike, Xander, and Jonathon Archer. Word of God confirms that he was at least bisexual, but never got around to acknowledging it to himself — thus why it was never acknowledged on the show. The actor who played him is gay, so had some fun with adding this to the character.
Jonathan seemed very close to Andrew, especially when they were in Mexico, where they slept in the same bed.
The writers couldn't decide whether Willow or Xander should be gay at the start of the series, so both of them fell into this category at times (most notably, Xander being Mistaken for Gay by Larry, and Willow saying "I think I'm kinda gay" in reference to her doppelganger). Eventually, Willow came out and Xander became purely heterosexual.
Xander still had moments of this after Willow came out, memorably in "Intervention".
Lorne, the Pylean demon from Angel, may be a much more subtle example of this trope. He constantly flirts with "Angelcake", but then again, we don't even know what gender he is, given that his mother looks like a huge bearded man. The actor stated that he always saw Lorne as an asexual character who enjoyed being alone with a few close friends.
Of course Stephen isn't gay! He's in a loving, committed relationship with his soulmate, Sweetness.
Combat Hospital: Dr. Grace Pedersen. When a female character flirts with her and asks her out, she only refuses because she's already taken (never mentioning said partner's gender), and she also claims to have her appetite for men spoiled by her husband.
Community: Dean Pelton flirts with and oggles men on a regular basis, but nothing definitive has been stated in any way. Plus Troy and Abed.
Dan For Mayor: One episode featured the titular Dan trying to win the support of an ambiguous conservative for his campaign. As he tries to interrogate the real estate agent for clues on his sexual orientation, the answers he gets are all the more ambiguous.
Eureka: Vincent. He's camp, he comments on a male character's attractiveness in the finale, and on the hypothetical attractiveness of "Joe" when he's forgotten Jo exists, and when the other male characters are talking about wanting to kiss Beverly he says "Even I've thought about it", implying this is unusual. Apart from that, he's more concerned with his cooking than relationships of any kind.
Niles on Frasierexhibits pretty much all the stereotypes, except that he's clearly deeply enamored with Daphne. Niles fits the trope so well in-universe that other characters occasionally assume he's gay (either not knowing about Daphne, or figuring that she's The Beard).
Game of Thrones: The eunuch, Lord Varys, especially when referring to his "Little Birds". The other characters lampshade this quite mercilessly, but Varys rolls with it. His Passive-Aggressive Kombat partner, Petyr "Littlefinger" Baelish, has this weird little obsession with Varys' nether-region, but his even greater obsession with Catelyn Stark shows that he's straight.
Loras Tyrell is depicted as quite flamboyant in the TV show, but in the books his sexuality is much more obscure
Gilmore Girls: Michel hit every Camp Gay stereotype (obsessed with his appearance, dotes on his mother, French!) but he did once mention a girlfriend (who went unseen).
This trope is explicitly explored with Coach Bieste, a rough and aggressive female football coach who's automatically assumed to be a lesbian. It's a bit of a plot twist when she reveals that she's 100% straight.
The Good Wife: Kalinda. The show likes to be ambiguous about it (or pretend that they are being so), but even though Kalinda has made out with guys while on cases, it seems strongly implied that she prefers ladies on her own time.
Heroes: In series one, Claire's friend Zach is never explicitly stated to be gay but all of the hints are there, and his big "I know who I am - I like who I am" speech doesn't leave much to the imagination. Then the whole "best friend has super powers and a serial killer after her" plot took precedence, his character was ignored and then he disappeared altogether.
iCarly: Sam is either this or Ambiguously Bi. She seems to like guys but none of them ever last past one episode, including the one in "iMake Sam Girlier" that such a big deal was made over. That episode also seemed to lampshade Sam's Butch Lesbian behaviors. Also, she and Carly have a lot of Les Yay. There is also speculation that Carly's brother Spencer might be gay, because of the episode where he was wearing a dress and dancing with cute guys saying, "I think I like it."
Justified: Tim Gutterson is a possible example. In "Veterans", he openly flirts with a (male) bouncer outside of a bar.
Tim: I love this shit. This shit makes me hard. Raylan: Well, now we've both been warned.
On the villainous end of things we have Wynn Duffy, who has an odd speech pattern, an obsession with women's tennis, sleeps in a beauty mask, and lives in his trailer with his male bodyguard, Mikey.
Just Shoot Me!: It's made fairly clear to the audience that Finch isn't gay, but his family have their doubts (most of the other characters though only played along to annoy Finch). Lampshaded in "Pass the Salt", in which one of his macho big brothers is revealed to be gay instead.
Keeping Up Appearances: It was a running joke that Hyacinth and Richard's son Sheridan, who lives with a man named Tarquin (who makes his own curtains, wears silk pyjamas, and has won prizes for embroidery), is possibly gay. Hyacinth however seems blissfully oblivious to the fact, and its heavily implied that Richard either simply pretends not to know for his wife's sake or just doesn't care if his son is gay; he's only bothered that he keeps phoning to ask for money.
The Larry Sanders Show: David Duchovny appeared twice against type as a version of himself whose words and mannerisms constantly had Larry wondering if he was coming on to him.
The Latest Buzz: Michael Davies. Being a kid's show, they can't actually state that he is gay but he is teenaged boy who writes the magazine's gossip column, is obsessed with fashion, and loves musicals (and sings the female parts). In second season they tried to move away from this characterisation by toughening him up and giving him an interest in girls, with varying degrees of success.
Ditto Olivia Benson, who looks like every lesbian stereotype, from one end of the spectrum to the other all rolled together and had the most incredible Les Yay with Assistant District Attorney Alex Cabot . Jossed in "PC". It probably doesn't help that their collected attractiveness, Alex and Olivia would make the most earth-shatteringly beautiful couple ever.
LazyTown: Robbie Rotten. Despite claiming to hate Sportacus and wanting him to leave the town, Robbie sure spends a lot of time talking about Sportacus, touching Sportacus and jumping into his arms whenever the slightly-above-average hero shows up.
Lewis: Sergeant James Hathaway of refuses to draw neat lines between sexualities or tell Lewis his own orientation. A former seminary student before joining the police, Hathaway seems conflicted about religion and sexuality.
Mad Men: Salvatore falls under this trope for about six episodes before he's resolved as, ah, unambiguous, but that has more to do with the decade he lives in than with maintaining any kind of tension. Compare this to the episode where a more minor character, a copywriter from Europe, very unambiguously outs himself to his coworkers; one look at Sal's face tells you that he was comparing their situations.
Malcolm in the Middle: Dabney and Lloyd, Malcolm's two effeminate classmates who like to talk about his eyes and think he is "handsome".
It's obvious to those in the universe; Cynthia even brings it up while she and Malcolm are watching the two of them eat lunch. Cynthia claims she can read lips, and fills Malcolm in. It's never determined if she can actually read lips or not.
Reese, particularly in the latter seasons as well.
The Mighty Boosh: Vince Noir was like this until he was revealed to be Bisexual in the third season.
Murdoch Mysteries: As James Gillies and his best friend Robert Perry depart from the police station for the first time in "Big Murderer on Campus," James touches Robert's back in a manner which may suggest that there is a greater intimacy between the two of them. Inspector Brackenreid wonders out loud, "Just good pals, or something more?"
Mystery Science Theater 3000: Depending on what "mood" they were in, Servo and Crow can qualify, even attempting to get married at one point. However, considering they are robots, they often do not "understand love".
"Brain Guy" Observer was a bigger example of this trope, going into the ladies' restroom with Pearl, dressing up in a stereotypical leather outfit for a "hot date", and refusing to seduce a woman:
Observer: Oh oh oh, no no, I could never seduce a woman, Pearl. Pearl: Oh, because you're... Observer: I thought you knew! I am completely, utterly... without a body. Pearl: Well, thank you for coming out with that information.
The Office: Michael Scott. His unusual obsession with Ryan the temp leads to hilarious moments, such as saying he would have sex with Ryan during a 'who would you sleep with' game, and disturbing moments, like intently peering at Ryan behind the blinds of his office space. Came to a head in Gay Witch Hunt when, to show he is tolerant of gays, tried to kiss Oscar against his will.
That's Just Me: Monica always pretends to be straight and says she's both bisexual and asexual, although her more masculine traits says something else....
Elizabeth's ex-boyfriend Steven loves pink and yellow and girly shows to the point of almost everyone questioning his true sexuality. Even Elizabeth makes fun of him for it.
Also, he tricked Elizabeth for a long time by pretending to be a woman named Stephanie....
Most girls on this show are super close. Bridget and Joanna have a fake marriage with Anika, Monica is the submissive worker of Hannia, Bridge, Anika, and Tsering, and Lela says some weird things to Joanna...
Most notably was in We're Moving?! But We'll Need a Truck was when she hugged Joanna from behind and asked if she wanted a massage.
Power Rangers Lightspeed Rescue: Kelsey. While she is on the femme side of butch, she is an extreme sports junkie, and she got very close to an astronaut named Nancy. Vida from Power Rangers Mystic Force on the other hand, is very awfully butch for a ranger based on a butterfly (it was a fairy in Magiranger, by the way), was made into a Lesbian Vampire, and at the end of the series when said vampire was turned human noted loudly how hot she became.
Kelsey is debatable, as when Chad said Marina was "the one" for him, Kelsey is clearly upset. She could just be feeling sorry for her friend, or...
Pretty Little Liars: Alison constantly flirts with Emily , the (then) closeted lesbian who was in love with Alison. It's unclear whether Ali was faking all of it, as Emily was something of a Morality Pet for Alison.
Not to mention Mona, who became A for the sole purpose of having Hanna all to her self. The show never explictly states whether or not this is in a romantic way, but Mona does seem very obsessed with Hanna.
Rules of Engagement: A recurring friend of Jeff is this in his first episode, and both women concluded he was gay, whilst both guys did not.
Saturday Night Live: Parodied this with the "Lyle the Effeminate Heterosexual" sketches, in which the title character would lisp and mince and prance his way through the sketch — and then object loudly whenever somebody insinuated he was gay. Among those led astray by his mannerism were his wife and son.
SNL also has Mango, played by Chris Kattan. Mango is a male exotic dancer who performs in a strip club. Though effeminate, Mango is adamant that he isn't homosexual, claiming that he stripped to support his wife and children. For what it's worth, one sketch showed his wife and children on screen.
Of course there was also the West Side Story-cum-Grease parody involving him in high school, where one of his song lines was "Boobies give me the creeps." It seems to be whatever is funniest at the moment.
The Ambiguously Gay Duo originated as a animated sketch on SNL and, as such, are detailed further in "Western Animation" below.
Seth Meyers on the Weekend Update segments with New York City correspondent Stefon (played by Bill Hader). Meyers always tries to rebuff Stefon's advances by saying he has a girlfriend, except for the last segment on the season 38 episode hosted by Ben Affleckwhen Stefon breaks up with Seth and Seth stops Weekend Update to stop Stefon from marrying Anderson Cooper.
Scrubs: The Todd began as a hyper-straight chauvinist pig. Later episodes heavily implied he was either a repressed or overcompensating homosexual. Then the hints were that he was a full-blown omnisexual unconcerned with any orientation, until one episode explicitly stated it.
After the Todd appreciates half a dozen widely varying people in as many seconds... Janitor: What are you? The Todd: I'm The Todd
SinCity: One episode featured the Mayor's nephew, who was basically a walking Camp Gay stereotype that loudly and obnoxiously hit on women at every opportunity, worked as a "closet organiser" and said the word "closet" roughly every three lines. Subverted at the end when he confides to Carter (the local token gay) that he was in fact 100% straight, but adopted an elaborte deception to create ambiguity as to his sexual orientation, because his parents desperately wanted to set him up with a partner (of either gender), and he preferred being alone.
Spaced: Brian Topp, who when questioned as to whether he's gay or not replies in the negative, but in a thoughtful tone of voice that suggests that if he's not gay, then he thinks he should be. Many episodes deal with his love-slash-lust for one of the female characters, but one episode also deals with the return of his platonic-love heterosexual ex-life partner.
Played up in several episodes, such as the one in which he "comes out" as an artist to his mother, who had been under the impression he was a lawyer because he thought his parents would disapprove of art. Her cheerful response - "Don't be silly, your father and I don't mind what you do, as long as you're not gay!"
See also the more extensive entry for Garak under Always Camp.
Also it was explicitly stated by the actor later on that he played Garak as omnisexual.
Supernatural: Angels are supposedly genderless and asexual, but Castiel's willingness to sacrifice everything for Dean makes a little more sense if you factor in something like vague romantic feelings, and Castiel usually wears an adult man, so he fits this trope. A lot of the characters (including Dean) comment on Castiel's body language around Dean, and a relationship between the two characters. On the other hand, his Foe Yay with Meg may push him more into Ambiguously Bi territory.
Tales from the Crypt: The mannerisms and speech of Beaks, the assistant of insane stage director Nelson Halliwell from the episode "Top Billing", just scream "gay". Of course, it could also be because he's insane as well.
Teletubbies: Tinky Winky carries a handbag, has a triangle on his head and is purple. He even wore a skirt in one episode. Parodied in The Simpsons when Homer dresses as one.
I'm Homie Womie, the Teletubbie. And I'm all man in case you heard otherwise.
Ugly Betty: Justin and Luigi Lombardi from the Mexican version La Fea Mas Bella; the Italian name is because Camp Gays in Mexico are usually given these kind of names. Interestingly, Mario Lombardi from the original Colombian version was more open but nothing near to flamboyant, having comparatively few mannerisms while talking about his boyfriends and male lovers quite openly; it seems that, in his case, calling him "gay" openly was a bit redundant. And Justin has the unique distinction of being, at most, thirteen years old.
When the show premiered, the actor playing Justin was just 11, and his Ambiguously Gay characteristics were essentially just a running gag. Once he got to high school age, the show starting fleshing it out more, with Marc, an openly gay character, becoming something of a mentor for him. After several arcs that never used the word "gay" but always heavily implied it, Justin was the first to speak openly about the issue by flat out denying it. However, when he and another boy started fighting over a girl, it became clear that they were actually more interested in each other, with their tension finally culminating in a kiss which finally brought him out of the "ambiguous" category.
Wizards of Waverly Place: Fans who don't think Alex is in love with Justin or Mason tend to think this of her, based on how she acts around other girls. Particularly with Stevie, who is less ambiguous.
In Season 1, Episode 3, the pocket elf has that familiar Lisp.
That's a case of the actor (Jack Plotnick) being gay in real life and using his real voice (which happens to have a lisp).