Mean Girls: Gretchen (the 'one small step from a complete nervous breakdown' version, rather than the 'empty inside' version).
Why should Caesar just get to stomp around like a giant while the rest of us try not to get smushed under his big feet?! What's so great as Caesar, hm? Brutus is just as cute as Caesar, Brutus is just as smart as Caesar, people totally like Brutus just as much as they like Caesar, and when did it become okay for one person to be the boss of everybody, huh?! Because that's not what Rome is about! We should totally just STAB CAESAR!
Carolyn Burnham from American Beauty is a prime example of this trope, subscribing to the adage, "In order to be successful, one must project an image of success at all times."
Katherine in Cruel Intentions pretends to be an upstanding Junior League-type schoolgirl, when in reality she's an oversexed, scheming coke fiend who takes out her frustrations on her fellow female classmates by persuading them to sleep around and ruin their reputations as a result.
From Toy Story 2, the Barbie dolls, whose gleaming smiles never falter, not even once. In the Hilarious Outtakes, one of them was complaining about how her face hurts from all the smiling.
The film version of the book Dangerous Liaisons (from which Cruel Intentions, above, was adapted) has the Contesse de Merteuil (Glenn Close) outright state that she learned to smile even when she didn't mean it.
Contesse de Merteuil: I learned to smile while under the table I was sticking a fork in my hand.
Played with in the film Far From Heaven in that the housewife genuinely had a wonderful cliche 1950s suburban life. Then it began to crumble around her....
Parodied with the camp counselors in the second Addams Family movie. Also, Wednesday's (fake) smile while at the camp, which is met with a "She's scaring me!" from another camper.
Speaking of Addams Family Values... What. About. DEB-BIE!?! Doesn't she deserve love? And jewelry?
The "Machine Man" in Metropolis when made to look like Maria, is a literal Type B (because she's actually a robot). Somewhat subverted because the main character figures out from her actions and the beliefs she espouses, but no one else does. She even laughs as she's being burned at the stake, before her true form reveals itself.
Tilda Swinton in Michael Clayton makes every effort to appear a confident and poised professional who loves her job, but behind the scenes she's a timid, nervous wreck.
Meryl in The Truman Show is an utterly creepy example of this trope. Almost everything she says is a sugary sweet soundbite that sounds like it could have come direct from a commercial, which gets even creepier when she's nattering on about coffee when her husband is on the verge of a psychotic breakdown. Of course, since she's actually an actress portraying the main character's wife on a 24 / 7 television show — and according to theWord of God, is a complete fame whore who gets a payrise every time she shills something successfully — practically everything she says is a commercial of some sort.
Janine in Animal Kingdom: she maintains a sugary-sweet maternal demeanor as she witnesses the criminal activity of her many sons, deals with the death of three of her children, plots to have her grandson murdered and blackmails a man into killing him.
Lucille Slocumb in Kingdom Come maintains the role of cheerful people-pleaser and peacemaker while under the stress of struggling with infertility, her recovering alcoholic husband, Ray Bud, planning her father-in-law's funeral, and dealing with a group of crazy relatives and friends. At one point she goes into a bathroom and downs "nerve pills". She finally snaps at the viewing when she comes across a bucket of chicken that triggers memories of a traumatic experience. The next day Lucille nearly has another breakdown when the funeral is delayed because of the preacher's "intestinal difficulty" and Ray Bud threatens to yank the bathroom door off the hinges, telling Ray Bud, "I don't have my nerve pills on me today!"
Karen from Love Actually is a more positive version of the trope. She tells one of her friends whose wife has recently died that he shouldn't openly cry because "people hate sissies". When she finds out that her husband bought his secretary an expensive necklace for Christmas she only cries in private but puts on a smile when she returns to her kids in the living room.
Elsa and Anna from Frozen are both Type A's, at least at the beginning. Anna is constantly cheerful and friendly despite her loneliness and desperation for someone that loves her, and Elsa constantly has to remind herself to "be the good girl you always have to be" for the sake of her sister and her kingdom, despite her misery. Anna gradually manages to become genuinely happy over the course of the movie as she finds friends and love, while Elsa is eventually pushed over the edge, which prompts her to toss away the mask completely.
Coraline has the Other Wybie, who was literally made to smile despite his actual emotions. So much so, that when he expresses his disapproval through a frown, the Other Mother sews his lips into a perma-grin. The stitches are cut, but not before we see what the Joker might have looked like as a child.
Gary King in The World's End, despite projecting a highly hyper appearance, is a depressed man who's aware he's lost any chance at a decent life.
Norman Bates from Psycho. Outwardly smiling and charming, but oh so unwell behind the mask. It's even more unnerving because Norman himself is so unstable that he acknowledges his Stepford mask slipping on and off:
Marion: Sometimes, we deliberately step into those traps.
Norman: I was born into mine. I don't mind it anymore.
Marion: Oh, but you should. You should mind it.
Norman: Oh, I do (laughs) but I say I don't.
From the Trope Namer, the 2004 version of The Stepford Wives had a gay couple, one of whom, played by Roger Bart was a male example. The main 'leader', played by Christopher Walken was one, too. Said male leader was a robot, built and programmed as "the perfect stepford husband" by Glenn Close's character to cope with her husband's adultery, and perhaps even her murder of him.
Chancellor Palpatine in the Star Wars prequels. On the surface, he was the amiable Chancellor Palpatine, but below...he wasn't.
John Candy's character Del in Planes Trains And Automobiles seems to be an indomitably chipper guy until it's revealed in the end that he's a deeply depressed widower.
The seemingly-kindly Lotso Huggin' Bear is actually a bitter old man (well, plush bear) who runs Sunnyside Daycare like a cruel prison warden, and has never gotten over being abandoned by his former owner.
Chuckles in Toy Mode, additionally falls under the Sad Clown trope.
The Chatter Telephone. Don't let his Fisher Price sticker-happy smile fool you, he's quite tortured inside.
Lenny in Strange Days maintains his chipper huckster facade in public, but in private he's deeply depressed.
Conner Rooney in Road to Perdition smiles when he is feeling shamed or humiliated, particularly when his father shows favoritism to Michael. When Peter asks him why he's always smiling, he leans down and deadpans, "Because it's all so fucking hysterical."
In The Dark Knight Rises, John Blake lost his parents at an early age, and practiced smiling in front of the mirror so that people would think he outgrew his "angry little kid" phase. This is how he knew Bruce Wayne was Batman. He recognized a fellow Stepford Smiler.
Mixed Gender Examples
Paul and Mary Bland of Eating Raoul are probably the world's most upbeat and together conservative couple ever, even as they descend into theft, murder and cannibalism.
"Bonjour! Bonjour!" The villagers in Disney's Beauty and the Beast sure seem to be a happy, friendly bunch...but they think Belle is a Cloud Cuckoolander in part because she's always reading and seems to be the only person in town who doesn't think anything of Villain with Good Publicity Gaston, whom everyone loves to the point that they help set up a wedding for him when he hasn't even proposed to her yet (and this doesn't even get into the cruelties heaped upon her poor dad, Maurice). By the end, this shallow bunch has become a Torches and Pitchforks mob headed off to kill the Beast because "we don't like / what we don't / understand / in fact it scares us / and this monster is mysterious at least..."
In Invasion of the Body Snatchers, being absorbed by the pods turns you into a Type B version of this. By the end of the movie, this happens to either an entire town or to the entire U.S., depending on whether you're watching the original version or the 1978 remake.
There's a rare humorous example of a Type B Stepford Smiler in Annie Hall, with a couple that Alvy Singer approaches on the street for relationship advice:
Alvy Singer: Here, you look like a very happy couple, um, are you?
Alvy Singer: Yeah? So, so, how do you account for it?
Woman: Uh, I'm very shallow and empty and I have no ideas and nothing interesting to say.
Man: And I'm exactly the same way.
Alvy Singer: I see. Wow. That's very interesting. So you've managed to work out something?
Chris and Belle in The Woman are a happy, successful, traditional couple with three children in the suburbs... who keep a feral woman locked in the cellar, ostensibly in an attempt to "civilize" her. And even before she came into the picture, there was a heaping helping of Domestic Abuse going on. Belle eventually snaps out of it once she realizes that her husband and her son are raping the feral woman.