American Flagg included a recipe for each story that showed Reuben Flagg's cooking Italian food.
Tintin: A comic famous for its research, such as when Tintin and the gang go to the moon with all scientific plausibility that the cartoonist, Hergé, could create. In fact, Hergé was notorious for his early Theme Park Version travelogue stories, until a friend convinced him to do serious research, beginning with Tintin The Blue Lotus. The result is a story in China that has been praised as an excellent primer for the China of the 1930s.
The best thing is walking through the Art/History Museum in Brussels and discovering e.g. the fetish statue from the "Tintin The Broken Ear" album.
Herge's drive for realism probably culminated in Tintin The Calculus Affair, where the amount detail put into background art and scene composition would have put a movie cinematographer to shame. In fact, in planning for a minor scene in the story where enemy spies force Tintin's car off the road into Lake Geneva, Hergé actually sent a employee to drive along Lake Geneva to find a location where assassins might plausibly force a car off the road.
In the same story, the fire truck shown after the house explodes was the exact reproduction of the actual fire truck of the town, down to the NUMBER PLATE.
Probably inspired by Hergé's example, anal-retentive amounts of research and detail has become a defining trait of the ligne claire comic artists.
Usagi Yojimbo: Stan Sakai likes to have an occasional story where he features various craftwork of Japan depicted in detail like swordmaking, cheating at gambling, kite making and pottery. It went even further when he devoted multiple chapters in a major arc to the legendary history of the famous sword, Kusanagi, before the eponymous hero came into the story. This devotion to proper research has earned Sakai a Parent's Choice Award for the comic for its educational value. Also, he often literally uses this trope by including a few paragraphs summarising his research on whatever was depicted in the comic in the letters section.
Many Batman stories written by Doug Moench, especially from the Batman flagship title, take unexpected sidesteps from the actual plot to allow for lengthy monologues or discussions of scientific, religious or philosophical nature. Unsurprisingly, even the discussions between two characters come across like the writer talking down to the audience.
Examples include: a museum security guard explaining the infamous Brontosaurus/Apatosaurus revision in Showcase '93 # 7, police lieutenant "Hardback" Bock giving a lengthy discussion about the origins and details of real-life alchemy in Batman # 546, and a detailed description of photosynthesis as utilized by algae in Batman # 367.
In fact, they've been doing this in Marvel comics for a while. Spider-Man, for example, often has tidbits about this or that, mostly about spider biology.
In one X-Men story involving the space shuttle nearly everything was correct - and this comic was written before the first time a shuttle actually went into space. Props to Chris Claremont!
Disney comics are not usually known for their accuracy, with one notable exception: Stories by the renowned comic book writer and illustrator Don Rosa often present surprisingly accurate and well-researched history, geography and even science (for example, if you see some mathematical formula in some comic of his, you can be pretty certain the formula is, in fact, real and accurate). Rosa is known for the amount of research he makes for some of his stories.
DuckTales especially demonstrated scientific principles quite often — possibly to make up for the fact that the main character was a talking duck.
In the collected edition of The Life and Times of Scrooge McDuck, Rosa notes out that he found specific points in time where certain historical figures would be in the same place. He also mentions when he has to "bend" the facts at certain points to make a better story, but it's fairly rare.
Just about every Silver AgeThe Flash story is solved using a random law of physics, expressed by Barry Allen (a forensic scientist) as a "Flash Fact". Wally West, thankfully, remembers the lessons from his days as Kid Flash, though now he has the Speed Force to help him with all the stuff that can't be done by physics.
A famous example of this in the Barry Allen period is when the Flash is fighting an alien who has a destructive sheath of fire around him. What follows is a science lesson of the natural ways to put out a fire with each failing against the creature's extreme heat, until the speedster realizes that fire cannot exist without air and runs around the creature fast enough to drastically lower the air pressure enough within the circle to put out the flames and suffocate the alien.
Like the Flash, a lot of the Silver Age Atom stories were heavily grounded in science and spent quite some time teaching it to the kids. One particularly extreme example is a story that essentially told the story of the telescope with a teensy bit of super heroism thrown into the middle.
Alan Moore loves to do this. Probably the best example is From Hell, which features a lengthy annotations section describing the research he put into making the comic & the truth (or lack thereof) behind the more fantastic elements.
Atomic Robo has an excellent basis in real world history and science. Brian and Scott often gush about the research they've done, and are the first to point out when they apply Artistic License.
Neil Gaiman does this a lot with mythology. He also has a tendency, though, to come up with things that sound like they came from actual myth or history, but he really just pulled out of his ass to fit the plot. Finding out which is which is part of the fun.
Gaiman pretended at the end of Dream Hunters that the story was adapted from the tale "The Fox, the Monk, and the Mikado of All Night's Dreaming", a traditional Japanese tale he had found in the book Fairy Tales of All Japan by Rev. B. W. Ashton while doing research for Princess Mononoke. This information was mentioned in almost every critique of the book. A few years later, Gaiman admitted in the preface of Endless Nights that he had completely made it up.
A similar example exists, though not based in mythology when he did research for American Gods. Having researched various cons for his con-artist character, he made up entirely the most overtly criminal of the cons - namely, stealing several thousand dollars from a bank. He was very surprised to find when someone actually copied the plan from the book and stole several thousand dollars from a bank. (Frank Abagnale Jr. did that in Real Life decades before Gaiman put it on paper, though it's unclear if he knew about it while writing the book.)
His Marvel 1602 really shows how much research he did into Marvel history, or just knew off the top of his head. For example:
Nicholas Fury describes his organization as England's "shield", a reference to his "S.H.I.E.L.D." organization in the regular comics. However, he also mentions that Peter Parquagh's parents used to work for him.
Not to mention this universe's version of Iceman: he changes his name from "Bobby Drake" to "Roberto Trefusis", then includes a brief scene where Trefusis mentions that he's a nephew of the famed seaman Sir Francis Drake. Sir Francis Drake actually was related by marriage to a family named "Trefusis", which Gaiman found out through some well-placed research into Drake's family history.
Garth Nix does something similar to the above, but it largely amounts to him throwing in every bit of cool-sounding mythology he can find. No one minds. In one of his books, he says how surprised he was when his editor informed him he couldn't use Aboriginal elements in his story because he was a white Australian.
Wolverine First Class had an issue about Wolverine helping a team of Canadian superheroes rescue the Governor-General of Canada, who was being held hostage in La Citadelle in Quebec City. It had accurate descriptions of Canada's government, fairly spot-on drawings of Canadian military uniforms, and a few nice bilingual bonuses.
Larry Niven did the prestige format "Ganthet's Tale" for Green Lantern, and inserted his own hard science twist to Hal Jordan's known abilities. Hal has to defeat a rogue green lantern, but they are too evenly matched. So Hal uses his ring to fly at near-lightspeed - backwards, away from the target. He then lets loose with a green energy beam of power. But because Hal is moving away at near-light, the beam is red-shifted, and transforms into a YELLOW beam, which bypasses the other lantern's defenses. This was used little if it all afterwards. Bizarrely enough, one of the few other places this turns up in was Superfriends, where Hal Jordan is able to free himself from a bubble created by Sinestro this way.
Clan Apis. Is a educational work that happens to also tell an interesting story. Jay Hosler is an entomologist/biologist and writes his works with education as the main point... though that's not to say that his works don't have a good narrative push. Another example of this is Optical Allusions and... well... you can tell by the title that he's done the research.
In Ex Machina, everyone slips statistics or historical factoids into their dialogue without missing a beat. Then again the main cast is the Mayor of New York City and his staff. Politicians are usually pretty good at spewing out statistics. This is lampshaded when Brian K. Vaughan and Tony Harris meet by a statue (yes, inside the comic) and Brian starts to say something about the statue, until Tony interrupts him and pleads him not to say random factoids.
Kingdom Come couldn't possibly have been made without the most intimate understanding of every facet of the DCU.
Mark Waid, the man who wrote it, is known as "the living, breathing DC encyclopedia" due to the insane amount of knowledge he has on The DCU; to the point where DC sometimes holds "stump Mark Waid" contests at conventions just to find out what he doesn't know.
George Woodbridge was a MAD artist for over forty years. He was also one of the world's foremost experts on historical military uniforms. Every time he drew military personnel, their uniforms were accurate down to the right kind of buttons for the time period.
Y: The Last Man often feature characters randomly spouting statistics about exactly how many women are involved in which professions in which parts of the world. This is probably the kind of thing lots of people would know, given the setting.
In 52 the writers intended to have ReneeMontoya be an actual alcoholic, not a light-hearted Hard-Drinking Party Girl. To help illustrate this, in one scene she takes a pair of aspirin while on a stakeout. The panel where she puts the pills in her mouth was specifically drawn to give the impression that she was chewing the pills and not just swallowing them; this is, apparently, "an old drunks trick."
Greg Rucka did a shocking amount of research on the geography, history, weather and politics of Antarctica for his first comic, Whiteout. The portrayal of the continent itself and the behavior of research stations and governments on its territory has been heralded as one of the most accurate depictions of Antarctica in American media.
Many of Mike Mignolia's Hellboy stories are essentially retellings of documented folktales, often using details that would usually be lost in modern versions. For example, "The Corpse" is mostly derived from "Teig O'Kane and the Corpse," which originally appeared in a compilation of Irish folklore edited by William Butler Yeats.
Before writing the Mega Man comic, Ian Flynn heavily researched the series, and it shows. Chest, Plum, and Ripot from the obscure Mascot RacerBattle & Chase appear in the first issue reporting on Light's new robots, that issue's Short Circuits has a Mythology Gag to both the cartoon and the hilariously bad American box art of the first game, and Fire Man retains his Southern accent from Mega Man Powered Up.
In James Stokoe's comic  The Half Century War, during a fight between Godzilla and Anguirus, the latter doesn't curl up into a ball like he did in Final Wars or any of the other comics, he instead turns around with his spikes pointing at his enemies and launches himself backwards. Also there's a lot of references and Mythology Gags to show Stokoe is not only a huge fan of the franchise, he also did a vast amount of research. Not only that but the way he designs the environments is very accurate to the time periods they happen to be set in.
In Godzilla Ongoing, it's mentioned by Boxer that the Endinburgh Castle is set over an extinct volcano which he and his team of monster hunters use to defeat Anguirus.
From the beginning, The Tale Of One Bad Rat was meant as a modern-day analogue of the life of Beatrix Potter and the Lake District or England. Bryan Talbot decided on sexual abuse as the reason for Helen running away from home as a simple reason, without thinking much about it. Then he started to research the psychology of abused children.