All over the place in Arata Kangatari. While the manga's story and action are very Shounen, with a Japanese teenaged boy switching places with one from a parallel fantasy world and going on an adventure in a Wutai-style fantasy land, the author is Yuu Watase. She's known for her Shoujo work, so many of the male characters boast well-defined muscles and their costumes make them Walking Shirtless Scenes. Even the translator gets excited during the Hot Springs Episode, making jokes about how it included some of the best panels of her favorite characters.
The entire male cast of Axis Powers Hetalia. It really says something when even the main character's grandfather has legions of Squee-ing fangirls.
Sechs from Battle Angel Alita: Last Order either fits the trope or is a parody of it. Starting out as a exact replica of the female main character, by volume 5 Sechs, after losing her original android body, has changed to a 1.8-metre-tall thin but muscular male body. This was either done to get more female readers into the series or to poke fun at the lack of attractive male fighters in the manga. Additionally, in volume 10 it's revealed that Sechs has gained a large female fanbase in the solar system, much to his/her annoyance.
If Black Butler's plot and gorgeous art doesn't keep you hooked on the series, the ridiculous amounts of Ho Yay fodder and gorgeous guys will. Special mention goes to Sebastian, who is, without a doubt, extremely badass, has silky shoulder-length black hair, is extremely tall and handsome, constantly wears black, has a somewhat sensual nature. And considering that his human looks are actually derived from Vincent Phantomhive's... Oh!
Creed from Black Cat qualifies for this trope rather nicely. Somehow, his evil plot to take over the world and kill everyone not up to his standards is justified by his sad Dark and Troubled Past involving his abusive mother. He has a rather deep and sexy voice, and there is no doubt that he would have no problems doing male-on-male things with Train. He also has an incredible amount of shirtless scenes (even his regular clothes show his chest). He also has a very naked bath scene where he's barely covered by strategic floating clumps of rose petals, in a slow pan from his feet to his head. And when he gets out of it, they pan as low as they can without showing "little Creed."
Ikkaku's shirt goes missing when he unveils his Bankai, Hisagi never wears sleeves and gets nicely roughed up in his fight with Findor Carias, Kensei has several scenes exposing his lovely, muscular chest and arms...the list goes on and on. Hell, even Mayuri had a Shower Scene that showed that he's actually pretty hot under his weird makeup.
Brave10 has a bevy of bishonen in scanty clothing but the Mr. Fanservice is Rokuro by a long mile. He's got crowds sighing over his prettyboy looks in canon, wears a Stripperific outfit which includes pairing a crop top with strappy low rise hakama that have ever-deepening hip windows and have been cut from Magic Skirt cloth, and he eventually gets an identical twin in the sequel, mostly so the author can draw them whipping each other's clothes open when they face off in the tournament arc and a bunch of Twincesty splash pages. To the author's apparent surprise, he was voted the most popular character when the magazine it ran in polled its readership.
Yarai in Cage of Eden. To recap: Yarai is tall, blonde, strong and has highly defined muscles and a big chest that make him the physically biggest character in the series. He has many Shirtless Scene and get a double-page where he bath naked.
Minami from Cherry Juice, who has the natural harem, the non-chalant shirtless-ness, and who is not above kissing his bishonen best friend in order to make his sister jealous. His status as this trope is lampshaded within the manga with the opening line:
Being a series about American football, Eyeshield21 have wonderfully fit athletes working out, shirtless, or just looking attractive all over the place. Special mentions go to Shin, Agon, Kakei, Mizumachi, Akaba and Kotaro.
While Fairy Tail rather blatantly caters to its male fans, it has one particular character by the name of Gray Fullbuster who, in addition to being the Only Sane Man, and having a tragic backstory, owns a very nice body which readers get plenty of chances to ogle, since his obligatory quirk is stripping to his boxers without realizing it. Hiro Mashima does not try to hide that attracting female fans is Gray's job. When the first major arc focused on Gray, he said it was due to the female fans: there weren't enough of them.
Natsu also qualifies as a Mr. Fanservice as his top consists solely of a vest, leaving his abs completely exposed. And Sting is always exposing his midriff. At one point, one of Sting's attacks seemed to accomplish nothing more than blowing a hole in Natsu's clothing just sizable enough for his abs to show through.
Elfman, any time he chooses to forego a top, which is often in the span of things. Sometimes he can be seen in nothing but a cloth that doesn't actually cover his ass.
For villains we have Jackal who has many fangirls surpringly. Azuma also, despite existing for only one arc, spent half of it shirtless and showing off a delightfully muscular form.
Fate/Zero's Lancer, Diarmuid ua Duibhne, which is an actual power of his thanks to his cursed Beauty Mark (which causes him tons of problems both in the original myth and in the show). The Einzbern Consultation Room short did not let this go un-lampshaded.
Zecchan: Why isn't there an otome game based on Celtic mythology yet?
Almost every single male character in Fruits Basket. Particularly Momiji, Yuki, Ayame and Kyou. The first wears the girl's school uniform (albeit not with a skirt) because "it looks cuter on him", and gets an Imagine Spot dedicated towards showing him aged-up as a Bishōnen. Yuki has soft grey hair and violet eyes, and made for a pretty convincing girl the time he's forced to wear a dress. Ayame is a white hair given quite a few Bishie Sparkle shots. Then there's Kyou, who fits more in the All Girls Want Bad Boys area, with a Hot-Blooded temper and tendency for dere dere moments around Tohru, and an apparent predilection for shirtlessness. The other males get their fair share of moments as well. Tohru lampshades this once, calling the Sohma family a "family of princes". Generally, the series — with its preference towards over-the-top romanticism and Dark and Troubled Pasts — aims more for making fangirls swoon rather than squeal, but the Sohma family curse's transformative effects lead to so much nudity that it still fits.
Sosuke Sagara is definitely the ultimate example for this show, though. He gets the most shirtless scenes, and in general is the one who is used when someone needs to look sexy.
With Fushigi Yuugi, it's probably just easier to narrow down which male cast members aren't catering to some estrogen brigade bait fantasies. Whether your taste runs to Draco in Leather Pants (Nakago, Suboshi), or to gorgeous, gallant royalty (Hotohori), or to fiery redheads (Tasuki) or to your basic romantic hunk (Tamahome), there will be at least one ridiculously attractive male character who gets a) gratuitously wet, shirtless or both; and b) a sympathetic Back Story. Hell, even resident monk Chichiri gets in on the fanservice action.
Lockon Stratos both Neil and Lyle, thank you very much, from Gundam 00. Somehow, both Shinichiro Miki and Alex Zahara manage to do wonderful things with Lockon's voice. It's possible that because he fits this trope so wonderfully that so many fangirls forget what happens when his Berserk Button is pressed...
What, ONLY the fangirls? Many 00 fanboys have claimed the Stupid Sexy Lockon meme for themselves, so smitten they are by his sheer badassery as well as his good looks. For some, if you're not gay/bi for Stupid Sexy Lockon, you're not a 00 fanboy — period.
Then again, this trope can probably be used to point out almost every male character in the series, protagonists and antagonists alike. In A.D. 2307, humanity is still at war... but at least they all look good.
In Hakuouki, nearly all of the high ranking members of the Shinsengumi are bishonen, with different members hitting all of the standard personality traits associated with this trope. Given the source material for the series, this shouldn't come as a surprise.
Higurashi: When They Cry: Keiichi. Aside from his various… interesting (and quite exploitative) outfits, he gets a now-quite-infamous Guy-on-Guy Is Hot scene between him and Satoshi in the Kira OVA, which is drooled over In-Universe by the female cast. Apparently, his dad is also one in the manga.
Although most of the male cast of Karneval could qualify to the point of being full of pretty boys, Gareki is especially seen in cut up or revealing outfits that should not look as hot as they do when he's wearing them.
JoJos Bizarre Adventure: Even most of the villains in the series look like they're models. For example, Caesar Zeppeli. Ever The Casanova, this guy regularly charms women with his good looks and smooth talking, both in universe and out.
Aikurō Mikisugi randomly slicks his hair back and removes his glasses to reveal his handsome face while also randomly undoing his clothes and striking erotic poses when he explains how Senketsu works to Ryuko. He does this for no reason other than to annoy Ryuko and make girls watching the show faint. Hell, he even has fangirls who find his old man disguise sexy, despite it clearly not meant to be.
Gamagoori is this for Bara Genre fans. He spends a lot of time shirtless and the show loves drawing attention to his size and muscle mass.
Tsumugu is this for similar reasons to Gamagoori. It helps that he's almost always near-nude.
In Kuroko no Basuke, pretty much all the guys are this. Considering that this is a sports-genre anime, this series has way more attractive male characters than other sports-genre series. From Kagami (with shirtless scene in episode one), Kise who works as a model, to Kuroko himself.
Mobile Suit Gundam Wing: Despite being part of a franchise generally targeted at men (because girls can't possibly be entertained by giant robots and politics), an overwhelming majority of the fanbase was women; women who were unabashedly interested in the male characters of the show for their looks, with maybe personality coming in at a close second. Heero, Duo, Trowa, Quatre, Wufei, Zechs, and Treize all fit this trope. The sheer amount of fanfiction, doushinji and websites dedicated to them (usually of the Ho Yay nature) is testament. IIRC this was done intentionally to broaden their audience demographic. It worked.
On that note; there is PLENTY of Dark and Troubled Pasts (particularly Heero, Duo, Trowa and Zechs), Badasses (all of them), pretty boys, questionable moments that fuel the massive amount of yaoi fangirlism, stoicism (Heero and Trowa; although they kind of sorta not really get over their absolute stocism), jerks with hearts of gold, and a Shirtless Scene (maybe — Heero had bandages, but bandages aren't shirts, right?). Depending on your mileage there is Foe Yay (Zechs and Heero always promising to finish their "duel"). So much Woobie (depending on the character it may be Iron or Stoic) it is almost painful to watch at times, considering what the pilots have been through and what they keep going through during the show.
Kou from Monochrome Factor. Troubled past? Check. Emotional and physical scars? Check. Sexy voice? Check. Looks great with his shirt off? Check. Comfortable with man-on-man scenes? Check. Akira and Shirogane are also great examples.
Despite being a gonk, Takeo from My Love Story!! is one of these. In the Beach Episode there's little focus on the girls but a lot on shirtless Takeo. The series subverts the usual image of his character design. His girlfriend Yamato finds his muscularity very attractive.
Kaworu Nagisa — the mysterious Fifth Child. Smooth voice, elegant, handsome, and for the few times he's appeared (counting the movies) usually he's either naked, giant and naked, wet, in bed with another guy or in any combination of those.
For the Straw Hats: Luffy, Zoro, Sanji, and Post-Time Skip Usopp. Luffy is handsome and reasonably muscular and his shirt is often unbuttoned; Zoro is ridiculously muscular and frequently appears either shirtless or in an unbuttoned shirt/coat; and Sanji is a slender Handsome Lech who was subjected to Even the Guys Want Him on Kamabakka Island. Post-Time Skip, all three of them have become even hotter, with Sanji gaining a small-but-smart goatee, and Luffy and Zoro both possessing more mature auras and additional scars. After the timeskip, Usopp has become incredibly muscular and much more confident, so he also qualifies.
This is kind of the reason why Saint Seiya has a BIG female fanbase.
The most obvious is probably Andromeda Shun, a Reluctant Warrior with a pretty face, in-universe fanclub and big brother complex. The storyline where he's possessed by the god of death doesn't help matters either.
The Sengoku Basara anime contains the gallons of fanservice from the original video game and adds a little more with an injured Date Masamune bandaged shirtless scene. Yowza.
Shokugeki no Soma is an advocate of equal opportunity for both male and female readers get the eye candy they want. The Cast Full of Pretty Boys is, by itself very fanservicey. The award though goes to Isshiki, who spends most of his screentime either in a Naked Apron or a Fundoshi (when he is working in the field), and the artist does not have a problem with shots of his ass and chest.
Gin, more appealing to the Bara fans, has a very muscular figure to which neither he nor the artist are shy to show off. He had a Naked First Impression with the main character, and they proceed to chat while wearing nothing but towels.
For those who prefer a more mature gentleman and a little adventure, Senzaemon Nakiri is both well-built and cut (in fact, he has pretty much the same body type as Gin), long white hair and a few facial scars, and strips whenever he is fed something sufficiently tasty.
And for those who like their men "mad, bad and dangerous", Azami looks good in a suit, and positively mouth-watering when training iaido in a gi just open enough to show the sweat running down his chiseled abs.
Blair. Admittedly, it was only during the Book of Eibon arc where all of the characters were gender swapped, but still.
Kid also qualifies.
And then there's Soul and Blackstar who each showed their abs at some points.
Soul mostly considering the scar across his chest, which included a slow pan up of his toned abs at first glance.
Space Dandy has both Ms. Fanservice and Mr. Fanservice— Dandy himself filling the latter role, as one can see in episodes 6 and 8. In 'The War of the Undies and Vests, Baby' Dandy spends 98% of the episode in just his briefs, and in the second half of 'The Lonely Pooch Planet, Baby' we get not one but two pan-ups showing his bare butt, as well as him dressed in just a towel.