In the West, gay men rarely appear outside of works aimed at... well, gay men. One of the cultural quirks of Japan (though it is slowly bleeding over to the rest of the world) is the use of young, homosexual male relationships as Fanservice for the girls. Works that focus on these relationships form a genre currently known by the English termBoys' Love, also called Yaoi.
But even outside of actual BL series, hints of male-male romance are often thrown in to help the series appeal to other demographic groups. Depending on the series in question, this can be limited to Homoerotic Subtext... or not.
A Yaoi guy doesn't need to be a Bishōnen, but there is a certain degree of overlap between the two character types. If there is a Yaoi Fangirl among the cast, she will try and invoke this trope.
See also Uke and Seme. For works where the male-male romance is the main dish rather than the garnish, see Boys Love Genre.
Spear Counterpart to Token Yuri Girls.
Note: couples from acknowledged BL series go on the Boys Love Genre page, please.
Has nothing at all to do with YaoGuai, thank goodness.
Axis Powers Hetalia has Germany proposing to Italy during the Buon San Valentino 2009 strip, red roses and tomato ring included. What comes of it is still unclear, but it's not really subtext at this point.
While Germany and Italy are "the" example of this trope, just about every male character gets this at some point.
Mei and Gabu in the Arashi No Yoru Ni anime film, although Mei's gender is ambiguous in the original storybooks and Mei's a girl in the recent CG series.
Rolo in Code Geass has more than a little of this going on towards Lelouch. It may be slightly more than coincidental that the character design was done by...
CLAMP. Pick a CLAMP series. Any series. More specifically:
Touya and Yukito in Cardcaptor Sakura and Tsubasa. Syaoran, for his part, has a huge crush on Yukito in the first half of the manga.
Fuuma and Kamui, also in X and Tsubasa. (Prone to touching each other suggestively during battle, and confirmed by Word of God to have been more than friends, although it should also be remembered that Kamui was initially in love with Fuuma's sister Kotori before she was murdered.)
Rikuou and Kazahaya, and Kakei and Saiga, in Legal Drug
Doumeki and Watanuki in XXX Holic - heavily implied, with Doumeki in particular exhibiting remarkable devotion.
Takeshi and Kentarou from Duklyon: CLAMP School Defenders. Kentarou often declares that his life's goal is to be a beautiful bride and he insists that he and Takeshi should go out on dates, get married, etc. Takeshi attempts to protest but never succeeds in getting Kentarou to desist.
In one episode of Excel♥Saga, the messenger sent by the heads of ACROSS is a handsome and somewhat androgynous rock star named Key. Excel becomes infatuated with him, and we are shown a fantasy sequence in which she imagines Key and Il Palazzo as Yaoi Guys.
Genshiken has Yaoi Fangirl Chika Ogiue, who in both manga and anime fantasizes about her love interest as a yaoi guy with another member of the club. In fact, the anime episode expands this out into a series of fantasies involving all the male members of the Genshiken as very bishonen yaoi guys, with a tragic romantic plot surrounding Sasahara and Madarame. Don't forget the Soba Incident, either.
Kazuki and Juubei from the Get Backers anime. (In the manga, any ambiguity in terms of romantic vs. platonic feelings is solely on Juubei's part.)
Shibuya Yuuri and Wolfram von Bielfeld from Kyou Kara Maou are engaged, sleep in the same bed, and are raising a daughter together. Second two resulting from Wolfram's fixation on the first. Played up for laughs, but taken very seriously by Wolfram, who has made passionate declarations of love to Yuuri.
The Mad Scientist Wars has it's fair share of pairings, but so far the most involved (read: Cannot Spit It Out) relationship is between Andrew Tinker and David Toboz. As of this example, they're official, but Andrew still is Genre Savvy enough to worry about It's Not You, It's My Enemies. Interestingly, Andrew's son may be heading towards such a relationship. Commander Xerox and Jess may or may not count. Jess is a shapeshifter who was born female, but when they first met she was shifted as a boy. Xerox, being Bi, donsen't seem to care much either way.
Kaworu Nagisa and Shinji Ikari's brief but powerful friendship at the end of Neon Genesis Evangelion is rife with common overtones of this sort. While not being specifically elaborated on, it has been milked in non-canonical (and humorous) material. Kaworu's (failed) attempts to get some attention from Shinji are actually canon in the spin-off series The Shinji Ikari Raising Project.
Actually, the creators have made it pretty clear that Kaworu was written to be Shinji's main love interest, even if their relationship was not given much screentime: earlier drafts for episode 24 had Shinji -almost- confessing his feelings for Kaworu (while skinny dipping), and a second draft even had a kiss scene between the two of them.
And in the Shinji Ikari Raising Project game (which has dating-sim elements), Kaworu's route is the main one, while the girls' routes are actually bonus.
Hikaru and Kaoru Hitachiin offer twincest-y BL fanservice to the customers of the Ouran High School Host Club. Honey and Mori's more downplayed guardian/master relationship has shades of this too. This is inadvertently pulled when Kasanoda finds out Haruhi's secret and leads the host club customers into believing he's trying to confess his love to the beautiful male Haruhi. After realizing she does not reciprocate he swears to be her friend forever—and suddenly becomes very popular with the ladies, who find his tragic spurned yaoi love to be cute.
Peacemaker Kurogane: After being raped in the manga, Suzu becomes gay, crazy, and obsesses over Tetsunosuke in this manner. And then there's this manga cover◊. Suzu's relationship with Tetsunosuke was always rather Homoerotic Subtext-ridden in the first place, although before it tended to be the more innocent sublimated kind... before it went into full on Stalker with a Crush. Bets are up in the air as to whether if Tetsunosuke had actually slept with Suzu after he was raped they would have been able to save a lot of pain.
Hijikata and Okita too.
Please Save My Earth includes a (heterosexual) couple who were both reincarnated as boys and who have to redefine their relationship once they find each other again.
Princess Princess is a series set in an all boys school where the most feminine boys are forced to dress up as girls and accept the adoration of the rest of the school. Some don't mind, most adjust. Shihoudani's mother, at one point, assumes that Shihoudani and Tohru are an item.
Akio Ohtori and Touga Kiryuu from Revolutionary Girl Utena represent this aspect in their series, especially in certain questionable situations. Interestingly, Touga himself seems to view it largely as a power game, while Saionji's role as his Patient Childhood Love Interest is less clear.
Saber Marionette J makes a running gag of the attraction the flamingly gay rich boy Hanigata has for the poor, industrious (and fundamentally straight) Otaru. Then again, they are on a planet whose human inhabitants are all men, clones in fact, while the women are, well, marionettes.
The uncensored first season of The NinetiesSailor Moon shows a romantic relationship between two members of the Dark Kingdom, Kunzite and Zoisite. This is largely censored in DiC North American release, mainly by turning Zoisite into a woman. In the Cloverway-dubbed fourth season Fisheye is also turned into a woman, despite having "her" take "her" shirt off in one scene. It doesn't help that in the original Fisheye's voice sounds like a girl's. There are a lot of other slashy subtexts in the later volumes of the Sailor Moon manga as well (although considering this is a well-rounded Shoujo manga, they're probably just covering their bases).
In Sensei No Ojikan, High School junior Kudou Yuuichi has had a crush on classmate Suetake Kenta since at least elementary school. He's an interesting example inasmuch as being a completely standard looking male student, unlike the show's (straight) part-time Wholesome Crossdresser.
To elaborate, in the world of Simoun, everyone is born female. The people of Simoun choose their gender when they reach adulthood. The men above were orginally together when they were female and remained together after they both decided to become male.
Vampire Doll: Dante and Hugo. Also, Aihara and Matsuzawa, two side characters who attend Tonae's high school.
Sion and Nezumi of No6. They've kissed on the lips (twice), they love to protect each other, they've held hands and intertwined fingers, they've cuddled, they've shared meaningful conversations, they've danced together, and they've slept together (not in the physical sense though). Also, Sion is quite willing to go into Yandere mode whenever Nezumi gets threatened or mocked and Nezumi has essentially claimed ownership of Sion in that one scene with the prostitute.
Raven and Lucius from Fire Emblem 7, with Heath and Legault as the second-most popular pairing. And it's not too much of a stretch to assume Matthew's got something for Guy.
It's more famous for the implied twincest between Ephraim and Eirika, but Innes and Ephraim could practically defineUST with their constant bickering in Fire Emblem: The Sacred Stones. Forde and Kyle are a toned-down version. Gerik and Saleh have a surprising amount of evidence in their favor: Shared history that they haven't really gotten over, the Sensitive Guy and Manly Man dynamic, and Gerik even takes Saleh out despite having two attractive women vying for his attention. In fact, pick any male character from Fire Emblem—odds are that they've got another guy they can support with for extremely subtext-heavy support conversations.
In the Heralds of Valdemar world, quite a few groups and cultures are quite open about homosexuality. Two of Vanyel's lovers (the first and the last) are widely remembered along with him and The Last Herald-Mage has him as its main character. The series main time frame also has Firesong, who seems unable to stay celibate very long.
The Noob webseries and comic treat the viewer/reader to what goes though Gaea's mind when she goes into Shipping Goggles mode about Fant÷m and Omega Zell. Her imaginary versions of the two fit perfectly.