Dani's House has S4 E9 Pen Pal with Jack's pen pal talking in a very fake Japanese accent. He's faking it - he's Cornish.
LOST has many examples, but the most prominent is in the pilot: Locke and Walt play backgammon and Locke mentions that it's the oldest game in the world and there's two players: one light, one dark. The final season reveals that the series' events revolved around two people, one "light" and one "dark", each having a goal that's part of what's essentially a game they invented in their childhood, and they've been at it for two thousand years.
The first time we see Juliet's face, it's her reflection in a mirror. In season 5 she sacrifices herself believing it will create a Mirror Universe.
Desperate Housewives had one example in the first season: Martha Huber learned that Susan burned down Edie's house, and blackmailed her over it. Seeing as how Mary Alice got a blackmail note and committed suicide over her secret, Martha's behavior toward Susan was a clue about the culprit. Eventually, Paul found out it was her who sent Mary Alice the letter and he killed her over it.
Teen Wolf's second season opening sequence is, basically, nothing but this.
In a truly epic bit of foreshadowing in the season three premiere Anne, Lily (from Lie To Me) tells Buffy about how she used to follow around this "loser preacher". Could she mean Jacob in season seven?
"I'm so evil and skanky. And I think I'm kinda gay." — Willow Rosenberg about her vampire doppelganger, a year before she didbecome gay — and three before she almost destroyed the world. It results in something of a terrifying echo, especially if you watch the second season again after knowing what happens. When Willow first utters 'Bored now' as a vampire, it actually gives you chills.
This example is particularly hit home by the exchange that takes place immediately after.
Buffy: Willow, just remember—a vampire's personality has nothing to do with the person it was. Angel: (who is a vampire) Well, actually... (Buffy gives him a Death Glare) ...that's a good point!
Word of God says they hadn't planned to make Willow gay as of The Wish let alone even earlier in Phases, but then there's this exchange:
Buffy: What guy could resist your Willow charms?
Willow: At last count? All of them, maybe more.
Similarly, Dawn Summers' arrival was foreshadowed by dream dialogue in two different episodes in season four: In "This Year's Girl," Faith and Buffy are making a bed in Dawn's future room when they have this exchange:
Faith: Little sis coming. I know.
Buffy: So much to do before she gets here.
And in the season finale "Restless", one episode before Dawn's appearance, Tara urged Buffy to "be back before Dawn."
There's also a remark somewhere about "trying on big sister's clothes".
Want to get even creepier? Faith steals Buffy's credit card and reads out the expiration date as May 2001. Now watch The Gift, airing May 23rd 2001.
Xander dresses as a pirate in the season six episode, and then in the seventh season he loses an eye and has to wear an eye patch.
There's a very subtle one during the first season where Buffy is hanging out with her friends and she says bite me. Cue Angel looking all weird at Buffy.
At the end of "The Harvest" Angel appears to be standing next to a sign saying WATCH YOU — appropriate enough for his Mysterious Watcher role. But when he walks away we see the sign actually reads WATCH YOUR STEP, foretelling his Face-Heel Turn into Angelus. Similarly at the end of "After Life" Buffy's other vampire Love Interest, Spike, is standing next to a discarded door with a BEWARE OF DOG sign, hinting at the Destructive Romance to follow.
A very subtle, blink-and-you'll-miss-it example from the 4th season premier, foreshadowing Buffy's mother's death: Buffy tells Riley "I can't wait until my mom gets the bill for these textbooks; I hope it's a funny aneurysm."
In Season 5's "Crush", while Buffy and Xander are investigating the train massacre, Buffy sits down in one of the seats which has the chalk outline of a body drawn around it, foreshadowing her death in the Season 5 finale.
Word of God is that they originally considered making Xander gay, in which case his meetings with Larry in Phases and Earshot would have been this.
Any dream Buffy has involving Little Miss Muffet.
Anytime Little Miss Muffet is referenced, at all.
In the Season 7 episode "Sleeper", Aimee Mann sings a song called "Pavlov's Bell." During the next episode "Never Leave Me" the Scooby Gang discusses the possibility that Spike is being controlled by means of Pavlovian conditioning.
In Season 7, when we first see Amanda, she mentions having confusing feelings for a boy that bullies her, and the fact that she retaliates quite physical and effectively. Next episode we see her we find out she is a potential slayer, which is fitting considering the obvious parallels with Spuffy and the natural physical prowess of slayers.
In the Season 9 comics there is "Where's Willow?" on the cover of "Apart (Of Me)" part III. Later, she shows up at Giles' house.
The depths of Warren's misogyny were alluded to from his first appearance, where he specifically programmed April to feel pain whenever the two of them weren't together, and then ultimately proceeded to ditch her anyway.
In the episode of Warren's death, Rack tells him that Buffy is the last thing he needs to worry about (Willow being the first), Warren quips "Yeah, let's talk about my skin troubles!" And we all know how he what happens to him later.
Before the Wishverse, Buffy and Willow discuss how in different circumstances she might have become Faith. Later Wishverse Buffy shows up (who is who Buffy would have been had she not been loved). Turns out without her friends, she's even worse.
Wishverse!Buffy is foreshadowing for Spike's Breaking Speech in "Fool for Love", where he tells Buffy that without her connections to the world (family and friends) she'd be a Death Seeker.
One of Faith's first scenes is with a poster prominently displayed warning about rape. Depending on how you count them she has at least three rape victims to her name.
Angel had its share as well. "Soul Purpose" in season 5 pops to mind rather quickly. When Fred is doing surgery on Angel in his coma-dream, she looks in and tells him "there's nothing left, just a shell". Although mainly referring to Angel, it was likely also a reference to her becoming a literal shell for Illyria several eps later.
In the same ep, Gunn growls like a cat during another dream scene. In "A Hole In The World" the White Room's cat conduit takes the form of Gunn himself.
Earlier in season 3, Wesley has a talk with Gunn about "the pull of conflicting loyalties". This is a kind of foreshadowing of Wes's own conflict with Connor and the team.
Highlander foreshadowed Richie's immortality in the first ep, after the defeat of Slan.
Connor: He will need watching.
We did find out later that immortals can sense pre-immortality faintly, so it's probably justified.
Charmed's Season 3 finale gives Prue Halliwell the line, "This has to end now or our lives are over!" At the end of the episode, she dies. Permanently.
From the season 2 episode "Morality Bites" when future Phoebe receives a premonition of how she killed a man, she is seen floating up into the air. In season 3 she gains the power of levitation.
Friends: Some may be a bit far-fetched in retrospect but:
Chandler and Monica's relationship beginning in the Season 4 finale: Several previous episodes hint at the possibility, and often near the end of a season. In the Season 1 finale Chandler offers Monica a Fallback Marriage Pact and she laughs, in the Season 3 finale Chandler offers to be her boyfriend and she laughs...cue the season 4 finale they're having sex, season 6 finale he's proposing and season 7 finale they're getting married.
There are other occassions seperate from these that foreshadow their relationship like Chandler calling Monica the most beautiful woman he's ever known [in real life] in a flashback when they almost sleep together. (When they actually sleep together he say's she's the most beautiful woman in most rooms). He also shows a preference to take off her bra over the other girls in Season 3, she gives him sex advice in Season 4 (when they get together he's 'the best she's ever had') and their No Sense of Personal Space habits throughout the first half of the series. As the writers claim they had no plans for Chandler/Monica its tricky to tell if it's Heartwarming In Hindsight or actual foreshadowing.
Ross and Rachel: From the very first episode, although that's pretty obvious as the show (especially during its beginning) is basically about them.
In a 2nd season episode, Ross mentions he likes that name. Two years later, he meets an English girl called Emily, who then becomes his second wife.
Rachel's baby's father: It's a bit suspicious that there's no major interaction between Ross and Rachel during the 7th season's last episodes (i.e. after they slept together and when she realizes she's pregnant) and the 8th season's premiere. Then, on the 8th season's second episode, she mentions the best sex she ever had with him. Guess what's revealed at the end of that same episode?
Even better, especially on rewatch: in TOW Joey's new brain, Joey mentions that Ross hasn't had sex in three and a a half months, to which Rachel reacts with a wink. In the same episode there is an interaction about not sharing secrets. This must have been shortly after the conception.
Dawson's Creek, especially in the third season and regarding the Pacey/Joey/Dawson love triangle. It's mainly foreshadowed in dialogue between Pacey and Jen, with lines such as "the sidekick never gets the girl" or "what does (Joey) have that all men seek her?" (or something to that effect).
Beverly Hills 90210, third season as well: Dylan seems oddly concerned about Kelly dating a guy he thinks is not good enough for her. Then, when Brenda leaves to Paris, Dylan is seen walking with Kelly. Then guess what happens...
Extensively used in Babylon 5, noted for having a pre-planned five-year arc.
For example, characters often say "Watch your back" to security chief Michael Garibaldi during the first season ( said character is then shot in the back in the first season finale). Almost every company mentioned in the series becomes somehow important in the storyline, even if they are used in throwaway lines in the beginning (Interplanetary Expeditions, ISN, Edgars Industries, etc.)
When Sinclair and Garibaldi return from Babylon 4 he tells disappointed Susan that next time he'll take her. Of course later when they go back through time to steal Babylon 4 he leaves Garibaldi on the station and takes Susan.
When Mr. Morden asks Vir what he wants. The answer is exactly what Londo does to him later in the series.
Or the Technomage's warning to Londo. Only a few episodes later Londo starts the Narn-Centauri war.
Pretty much all of the numerous visions in the show. Even if some aren't exactly what they appear to be...
Londo refers to his three hated wives as "Famine", "Pestilence" and "Death". By exclusion that leaves himself as "War". Guess who ends up escalating the simmering Narn-Centauri conflict.
Virtually all of Arrested Development's major plot twists are repeatedly hinted at long before they take place.
"This party's gonna be off the hook!" -Buster, one year before he loses his hand and gets it replaced by a hook.
That's not nearly as bad as "I never thought I'd miss a hand so much!" in reference to his hand-shaped chair.
Michael: I don't even have a girl, much less a stupid one.
Rewatch all the Tony elements of NCIS's fourth season in light of the context of the season five premiere. Then kick yourself for not spotting the gradual setup for The Reveal that his relationship with Jeanne Benoit is actually an undercover operation to get at her father, La Grenouille. In particular, the scene early in the season when Tony asks Director Shepard for relationship advice takes on an entirely different and kind of creepy subtext that is not evident the first time around.
Also, Gibbs' furious reaction at the end of the second season premiere takes on a whole new meaning given the third season finale.
When Kate is held hostage by Ari in the first season finale, Gibbs suddenly imagines her dead via headshot for a moment. Exactly one season later in the second season finale, Ari snipes Kate dead, and she falls to the ground in an identical scene to the one Gibbs imagined. This however, actually wasn't preplanned as Kate was only killed because the actress decided to leave, which wasn't known until the 2nd season was already underway, making this an aftershadow of sorts.
The Wire has many cases of foreshadowing, but the two best examples are:
A conversation between three drug dealers in the first season about chess, and how the pawns get "capped quick", while the queen is the best because it's stable and "makes all the moves". By the end of the fourth season, all three of the participants in that conversation had died, because they were, like many of the low-level drug traffickers, simply pawns themselves.
In the third season, detective Bunk Moreland witnesses a group of children pretending to be stick-up artist Omar Little and his group of robbers, with one small boy constantly asking to play as Omar. Two seasons later, that same child, Kenard, would be the one to shoot Omar dead in a convenience store, the result of a surprise attack that was the calling card of the victim.
In Law & Order, just before the season finale where Serena Southerlyn is fired and outs herself as a lesbian, there was an episode where McCoy successfully argues to have gay marriages in the state ruled invalid to remove a claim of spousal privilege. Southerlyn's disgusted reaction to homophobic comments in the episode and refusal to even consider helping McCoy could be seen in a new light. Additionally, in the season twelve episode "Girl Most Likely," when the DA's have realized that the dead girl was murdered by her lesbian lover so as to avoid being outed by her, Serena talks about a "friend" who didn't come out until college, in a tone that makes it pretty clear, in hindsight, that the "friend" in question was herself. Plus, in the season thirteen episode "Seer," it's Serena who figures out that their key witness is a lesbian, and actually the killer, who murdered the victim because she rejected her advances. Why was Serena able to see something that everyone else missed? In retrospect, that Serena was a lesbian was actually foreshadowed pretty heavily.
Detective Stabler's exit from the show was heavily foreshadowed for many seasons: This being his angry and violent temper, and his rush to judgement. It got him in trouble in past episodes, but because of his popularity in the department and his faithful partner, Olivia Benson, he was able to keep his job. That is until the Season 12 finale episode "Smoked", where Stabler is forced to shoot a teenage girl who was armed and already shot two other people. Because of his past actions in previous seasons, it was easy for the higher-ups to believe that Stabler once again rushed to judgement and let his violent side get the best of him. He's placed on administrative leave until a full investigation was done, but Stabler decides to turn in his badge to avoid a major scandal.
Supernatural often has episodes which help set up future events in the series. For example, Dean's almost suicidal guilt over not dying in "Faith" happens on a much bigger scale over Season Two where his father dies for him. "Crossroad Blues" also sets up his actions in "All Hell Breaks Loose" where he's so guilty over Sam's death that he sells his soul for him.
Also from "Faith" is the reverend telling Dean that he chose to heal him because Dean has a very important purpose and it isn't over yet. Cue Season 4, when Castiel tells Dean that it's his job to stop the Apocalypse.
Season 2's Houses of the Holy is like a full episode of foreshadowing that not only will angels eventually be introduced, but that Dean will end up rather fond of them (or one). A priest even uses the term "...an angel of the Lord" which is how Castiel introduces himself to Dean in season 4. On the same topic, we find out at various points throughout the series that Dean's mother would often tell Dean as a child that "angels are watching over you". In season 8, Castiel straight up says to Dean's face "I'll watch over you".
Ruby tells Sam that she's a demon and manipulative is in her job description... the finale of the next season has her admit that she's been manipulating Sam all along. See also her quiet rebuttal to Dean that she doesn't believe in the Devil when her game plan was actually to free him because she believes that Lucifer will lead demons to Paradise.
Also, "Nightmare" sets up the end of "No Rest for the Wicked". At the end of "Nightmare", Sam's powers are triggered by seeing Dean die in a vision (he telekinetically moves a dresser out of his way). At the end of No Rest For The Wicked, he watches Dean actually die, and then his power apparently reawakens (Lilith can't kill him).
The supposed heartwarming moment (which now comes off as half-arsed) in "Nightmare" where Sam says that, all things considered, their Dad wasn't that bad (i.e incredibly abusive like Max's Dad) and Dean repeats the line in a strange tone sets up/is paid off by "Something Wicked"/"Dead Man's Blood" where we find out exactly how crappy John can be.
Not to mention Dean's seemingly out-of-character behaviour of hating the food and chucking the wrapper in the backseat in "Simon Said" and the love of the Hollywood/Prison food in "Hollywood Babylon" and "Folsom Prison Blues", which gets paid off in "What Is And What Should Never Be" where he's practically orgasming over his Mom's homemade food.
Several of Bela's seemingly-flippant/catty remarks in Season 3 actually make more sense upon a second viewing, including "We're all going to Hell, Dean. Might as well enjoy the ride", her response to Dean's snarks about her father and how damaged she is, and her theft of the Colt, setting up The Reveal in her final episode that she sold her soul to kill her abusive dad and is trying to get out of it by doing whatever the demons tell her to.
In the 4th season finale, "Lucifer Rising," when Zachariah reveals to Dean that his role as the angels' Chosen One is not to stop Lilith, but to defeat Lucifer, they are standing in front of a painting of the Archangel Michael with his foot on Lucifer's neck. In the 5th season premiere we learn that Dean is the intended vessel for the Archangel Michael.
Demons on the show are known to have telekinesis. In the 9th season, Dean received the Mark of Cain from Cain (now a demon), in order to use the First Blade against Abbaddon. During his fight with her, he was able to use telekinesis to pick up the blade from the floor. Now, guess what he turned into in the season finale?
The new Doctor Who series always foreshadows its season finale as early as the second episode of the season. It uses, however, very (very, oh so very) cryptic foreshadows like "Bad Wolf" or "Doctor-Donna". Whenever psychics are in, expect to hear a lot of complete nonsense that will finally be put together in the final episode.
In the Series 3 episode "Utopia", the whole episode is pretty much foreshadowing of the return of the Master
Which started a lot sooner than that: when the Face of Boe tells the Doctor You Are Not Alone, many fans' thoughts instantly jumped to the Master.
And far away, across the universe, on the planet Crafe Tec Hydra, one side of a mountain carries carvings and hieroglyphs, crude representations of an invisible War. The artwork shows two races clashing, one flesh, one metal; a fearsome explosion; and a solitary survivor walking from the wreckage. Solitary? Perhaps not. Under this figure, a phrase has been scratched in stone, which translates as: You Are Not Alone...
A very subtle bit of foreshadowing happens in the Christmas episode of Season 4. When the tourists of the Titanic teleport down to Earth for a brief visit, the temporary companion for the episode, Astrid, exclaims that there are no stars in the sky! The season long story arc of Season 4 centres around the stars disappearing in the sky. Russell T. Davies, I never knew you had it in you.
The taxi which tries to pick up Stacey Campbell in "Partners in Crime" has an ATMOS sticker, a blink-and-you'll-miss-it piece of foreshadowing to "The Sontaran Stratagem".
"Silence in the Library" foreshadows "The Time of Angels" (and presumably a few more) through a throwaway line from River.
Series 5's "The Vampires of Venice" ends with the villain of the week telling the Doctor to dream of her and her race, a subtle foreshadow of what the next episode is about.
And in the next episode, watch what Rory replies after the Doctor says "I've crushed your flowers". He replies "Oh, Amy will kill you". Later on Amy and the Doctor commit suicide to get out of the dream, with Amy driving the car into the house at high speed.
In "The Hungry Earth", Rory goes to put Amy's engagement ring back in the TARDIS for safekeeping, saying "Go on, I'll catch you both up". At the end of the double episode, Rory is killed. By "The Pandorica Opens", however, he's been resurrected as a Nestene duplicate, thus "catching up" to the Doctor and Amy later in their time-stream, also, in "The Big Bang" he then waits for nearly two thousand years beside Amy's stasis-locked corpse for the Doctor and Amy's younger self to show up and re-animate her. He caught up with them twice!
Although the Classic series wasn't done in the same cinematic style as the new Doctor Who, there is subtle foreshadowing to be found (some of it may be unintentional though).
The Third Doctor's regeneration may have been foreshadowed by Sarah Jane in The Monster of Peladon. In one scene she says, "The Doctor always says that while there's life, there's..." She trails off, letting the sentence hang in midair, the word 'hope' left unspoken. In the very next episode Planet of the Spiders, the Doctor's final words to her are, "While there's life, there's..." He loses conciousness just then and never finishes the sentence. He regenerates a moment later, making those his last words before his 'death'.
In the series 7 episode "The Angels Take Manhattan", Rory leaves himself vulnerable to attack by a Weeping Angel when he's momentarily distracted by a tombstone with his name on it. This foreshadows the finale, "The Name of the Doctor", in which the Doctor says that the one place a time traveller must never visit is his own grave, which the Doctor is forced to do that episode.
Clara also violated that one rule, before she was even a permanent companion: the first time we see present-day Clara, she is standing by a tombstone for her Victorian version.
The Eleventh Doctor's regeneration episode reveals that his entire tenure as the Doctor had been rife with foreshadowing, literally from day one: the crack in Amy's wall turned out to be caused by The Time Lords trying to get back to our universe. Or, more accurately, caused by the Silence blowing up the Tardis to try and stop the Doctor from bringing the Time Lords back to our universe, inadvertently giving them the very passage they needed.
Day One of Torchwood: Children of Earth had an incredibly blatant and yet easy to miss piece of foreshadowing in this bit of banter by Jack and Ianto:
Ianto: You are going to get us all killed.
Jack: No, you get killed, not me. You die like a dog, like an ugly dog.
Strangely, the much maligned decision to turn an entire season of Dallasinto a dream seems to have had plenty of accidental Foreshadowing. The 'Dream Year' has a strange, slightly surreal air completely at odds with the rest of the show as noted in this article.
In the revival of Dallas several were made to Rebecca being Cliff's daughter.
Starts with Rebecca and Christopher go to meet Cliff in "The Price You Pay", and Rebecca acknowledges Cliff with a long look and stilted greeting to each other when they first meet. This later gets picked up on when it's revealed that Rebecca is Cliff's daughter, and she was in on the plan all along to take Christopher's drilling technology.
Also in the final episode Rebecca is happy when Christopher brings Chinese food which in the original Cliff was noted for having a fondness
House: In Season Three, Wilson's reasoning - he was afraid that House might think he was God and take an even bigger fall later on if he made a mistake - for his ill-advised, badly timed attempt at teaching House humility turns out to be well-founded when House pisses Tritter off in "Fools For Love" and utter disaster ensues.
In one of the many Season Four examples foreshadowing the finale, when the Hospital Inspector tells House that he's heard his name before, House replies that most people have because his name is also a noun. In the finale, the mystery woman's (who is really Amber) amber necklace helps House solve the mystery of who's dying.
Each season finale foreshadowed the Season 5 finale, with increasing obviousness.
Firefly has several foreshadowing moments. It is possible that some of them never were fulfilled, because of the cancellation.
In the pilot there are two. 1) Jayne tells Mal that Dobson tried to bribe him, but didn't accept because "the pay wasn't good enough". In Ariel, it was. 2) Kaylee asks for a new compression coil for the engine, warning that they'll be adrift in space if it breaks. That happens in Out of Gas.
River sometimes repeats "Two by two, hands of blue". The two agents who hunt River have blue gloves.
And in Ariel, though it looks like River's attack on Jayne is just regular River craziness, he IS wearing a Blue Sun t-shirt at the time...
When Simon mentions Early knocking out Book, Early says "that ain't no Shepherd" in Objects in Space. Book also seems to be come kind of Alliance VIP, as shown by their willingness to give him medical aid.
When coupled with the subtle hints in 'Serenity' that Book had at some point been an Alliance Operative like the one in the film (explaining their eagerness in the above point), this could have been a foreshadow of plot points Joss Whedon wished to expand on later in the series. The comic 'Serenity: A Shepherd's Tale' provides another possible version, this time as an Independent mole in the Alliance navy who killed the real Book and took his identity, later becoming a Shepherd out of guilt over his crimes.
In the first episode "Serenity", when the ship is about to be boarded by Reavers, the camera cuts to a scene of Inara taking out a syringe of some description. Later in "Out of Gas", Inara utters the line "I never want to die at all", and in the flashback is noticeably cryptic as to why she wants to work on Serenity rather than a luxury liner. All foreshadowed the fact that Inara had a terminal illness, and was aboard Serenity as a means to see more of the world before her demise. The payoff was never revealed though, due to premature cancellation. Confirmed by Word of God.
A good one in "Trash" when Simon confronts Jayne about his betrayal on Ariel. After Simon leaves, River, in a seemingly funny and Cloud Cuckoo Lander statement, says "Also, I can kill you with my brain". The significance of this statement is revealed in "Objects in Space" where River's intelligence, creativity and strategising comes together to defeat Jubal in a giant Crowning Moment Of Awesome.
In the Freaks and Geeks pilot, Nick declares, "Disco sucks! I hate disco!" The show's final episode sees him wholeheartedly embracing disco culture.
In the Halloween episode, the geeks go trick or treating and receive circus peanuts from one house. Bill asks the woman "Do these peanuts actually contain peanuts? Because if they do, I could die." Later in the season, Bill ends up in the hospital and almost dies after a bully tricks him into eating peanuts.
The Heroes Season One episode "Five Years Gone" foreshadows much of Volume Four, "Fugitives".
Law & Order: Criminal Intent. In "The Healer", a voodoo priestess warns Det. Logan: "You think before was bad, Detective? Just you wait." In Logan's next episode, "To the Bone", Logan shoots an undercover cop, which leads to Captain Deakins being accused of recommending a promotion for a cop in exchange for backing Logan's account of the incident (in fact, Deakins was set up by Frank Adair, a former friend & ex-cop, whom Goren and Eames arrested for murder in "My Good Name".) As a result, Deakins resigns.
Smallville has allusions to the classic Superman almost as often as spoken dialogue, many of which may count as foreshadowing, although it is more or less a Foregone Conclusion. The Smallville wiki has a list of how many times they do this. Right here.
NUMB3RS. In the episode "Dark Matter", Colby gave a detailed explanation of technology used in school ID tags to track students. Everyone else stared at him and he explained that he read it in a magazine. At the end of the season, it's revealed that's he's a Double agent for China. So, someone like him would know a great deal about tracking technology.
In the first episode of the second series of Primeval, Cutter says to Stephen: "You think I would have just stood by and watch you get torn to pieces?" which is exactly what happens at the end of the series, except Stephen was behind a door only he could open.
In The X-Files, there are several obvious moments foreshadowing Scully's cancer in season 4. But one quite subtle one is in the episode 'Unruhe' where a crazy guy tries to lobotomise her to remove what he calls 'The Howlers' that are causing her 'unrest'. When he points to where the Howlers are, it's the exact spot where her cancer is.
True Blood has many examples; some apparently innocent and casual statements pronounced by usually secondary characters foreshadow lots of future events. Basically if somebody says something that "could" happen, it will.
One night, Hoyt tells Sookie that he likes her relationship with Bill and even asks if he has a friend of his age he could date. Turns out that Bill does; Jessica. Guess what happens between them.
In season 1's last episode the cast is watching the news where it's announced that vampires marrying humans is now legal in Vermont. Arlene, a secondary character back then, innocently teases Sookie about the fact that she can marry Bill now. Sookie tells her that she wouldn't know what to say if Bill proposed to her. And that's exactly what happens in season 3 when Bill finally does ask Sookie to marry him.
At the start of an episode of Noah's Arc, Chance is giving Noah advice that there's always a time when a man has to choose between his principles and his paycheck. During the next episode, Chance has to choose between helping a lesbian couple and allowing Eddie to keep his career (one of the lesbians is Eddie's boss's wife).
Many assumed that Roseanne had jumped the shark in its final season, as things got sillier and more unbelievable. Then came the Downer Ending that revealed that the entire season, and a lot of the series, was Roseanne's fictionalized (with a heavy dose of Wish Fulfillment) autobiography that she started writing after Dan died of his heart attack. The real foreshadowing, however, is that VERY early on in the series it was shown that Roseanne had wanted to be a writer, but that her plans had been derailed by marrying Dan and having kids.
One example of the subtle variety came from leg 2 of All-Stars, where, upon leaving the Detour at the same time as Eric & Danielle, Rob said that even on Eric's best day, he had no chance of beating them. Rob & Amber were eliminated two legs later, while Eric & Danielle won.
In Season 1 of Gossip Girl, Blair breaks off her apparently casual relationship with Chuck because he manipulated everyone and didn't care if he hurt her in the process of those manipulations. She even says the line "This is why you and I can never work." Two and a half seasons later, when they're in a long-term serious relationship, he manipulates her into prostituting herself for his benefit, causing the most heart-breaking break-up of the series.
"Ua Hala", the second-season finale of the reimagined Hawaii Five-0, begins with a cop being set up for his murder by being lured to what he thinks is a dead body but is actually revealed to be a mannequin. This seems to be a subtle foreshadowing of the end of the episode, where we learn that McGarrett's mother, whom we had been led to believe died before the series, is actually alive.
In a flashback in the third episode of Person of Interest, "Mission Creep," Reese has a chance encounter with his former lover Jessica in an airport. In the course of the conversation, he tells her, "In the end, we're all alone and no one is coming to save you." Later in the season, in "Matsa Nyaya" and "Many Happy Returns," we learn that Jessica ended up in an abusive marriage. She made a desperate call to Reese for help, but he was on a mission and couldn't get there, and her husband beat her to death. She died all alone, because no one came to save her.
Also foreshadowed by Reese's opening narration from "Pilot," which he repeats in "Many Happy Returns" as he confronts Jessica's husband Peter.
Subtly reinforced in the second episode, "Ghosts," when Jessica's picture appears on one of the screens showing the people on the Machine's "irrelevant" list (people about to be involved in a violent crime, but not relevant to national security).
The West Wing: An episode opens on a newspaper story about how Josh, the president's deputy chief of staff and main liaison to Congress, is effectively his "101st senator". By the end of the day, he has actually lost his party a senator (a Dixiecrat defects to the Republicans).
How I Met Your Mother does a lot of subtle ones. Ted and his fiance Stella have a Nonverbal Miscommunication when Stella's sister informs them that her fiance ran off and she can't get a refund. Ted thinks their conversation is about the lunch. Stella thinks it's about taking the wedding. It's been noted that Lily and Marshall have perfect "couple telepathy", so when Ted and Stella have this miscommunication, it's an indication that they are not meant for each other and Stella ran off with her ex-boyfriend the day of the wedding.
Not to mention that earlier Future!Ted stated that his and Stella's relationship would end badly. He did the same when Present!Ted and Victoria decided to make their long distance relationship work, with Future!Ted commenting that it didn't.
Ted's favourite movie is Annie Hall where the titular character and the protagonist get in a relationship, have it end and decide they are Better as Friends. Sound familiar?
In season 4, Marshall says in 3-5 years, he'll be carving the Thanksgiving turkey with a lightsaber. The stinger for that episode shows him doing that 3-5 years in the future, talking to Lily and his mother. But not his father, who dies two years later before this scene would take place.
The "Bad News" is done in a Fridge Brilliance way. Most of the episode leads the viewers to believe that the "bad news" is that Marshall can't get Lily pregnant. It's all a ruse.
In the pilot episode in the first scene with Ted, Robin and Barney, Ted describes it in his head "like something from an old movie, where the sailor sees the girl across the crowded dance floor, turns to his buddy and says 'See that girl? I'm gonna marry her some day...'" Except he never finishes the sentence in real life because Barney interrupts him. This is clever foreshadowing because Ted doesn't marry Robin. Barney does.
One episode has Robin deciding to forsake dating and focus on her career, to which Future!Ted says "Ironically, that was the day that she met Don." They naturally get together but the real foreshadowing comes when Robin was offered her dream career but turned it down to stay with Don. Ironically, when Don was offered the same job, he chose his career over Robin.
JAG: In the pilot episode when Harm first arrives on the USS Seahawk both the Skipper and the CAG notices this from the tower and speaks on the phone where they hint at Harm's backstory.
American Horror Story: Asylum has a nice case of literal foreshadowing: take a good look at the poster for Asylum. Dr. Thredson is standing near the back of the room - now, who's standing where his shadow should be?
Sherlock foreshadowed the season 2 finale way back in the very first episode of the series.
Jefferson Hope: I'm not going to kill you, Mr. Holmes. I'm going to talk to you... And you're going to kill yourself.
Which, for all intents and purposes, is basically what Moriarty does to Sherlock, though the latter didn't actually commit suicide.
Sally: One day we're going to be standing around a body, and Sherlock Holmes will be the one who put it there.
In "His Last Vow", she's right.
This belief - which is espoused by almost all of Scotland Yard regarding Sherlock's "psychopathic" tendencies - is what allows Moriarty to pull off his Xanatos Gambit against Sherlock so successfully in the season 2 finale.
Sherlock finding John sitting gloomily in a graveyard in Hound of Baskerville also foreshadows the season finale.
Sherlock is seen standing on a large, tall rock in the same episode several times, foreshadowing how he's going to commit suicide in the next episode.
In Misfits, Nathan's power is first hinted at by his mother's insistence that "nothing anyone says ever hurts [him]". A later episode presents an alternate timeline in which Curtis wasn't around to help the rest of the Misfits escape their first probation worker. The only survivor of the incident is Nathan, who reveals that the police found him half-dead at the scene.
In Breaking Bad, a burned teddy bear pulls double duty, foreshadowing an air traffic disaster and Gus Fring's death.
In a mid season 2 episode, Jesse attempts to surprise Jane with breakfast in bed. When he comes back to find her awake, he says "You wern't supposed to wake up." She responds "Ever, or...?" A few episodes later, she dies asphyxiating on her own vomit while the two sleep off a heroin binge.
In the fifth season, Marie a couple of times while babysitting jokingly says she loves Holly so much she never wants to let her go. When Walt's secret gets out, she tries to abduct Holly for her own good.
Gilmore Girls has one in season 4 after Luke comes back from the cruise, during which he married his girlfriend Nicole
Luke: There's more.
Lorelai: Oh my God, she's pregnant! You finally reproduced!
Cue Season 6...
The episode Elsewhen of the 1974 Land of the Lost series may have foreshadowed this in the fact that Rani a future version of Holly who judging by appearances looks like she eventually got back home due to the absence of rough edges of any kind...read: she's gorgeous! departs giving Holly some wisdom to "Cherish her loved ones...they won't always be there." This could be simply interpreted An Aesop about the death of loved ones being part of life. With the abrupt and clumsy writing out of Rick Marshall in the first three minutes of the first episode of the third season, it could be interpreted as foreshadowing if you didn't know the circumstances regarding actor Spencer Milligan's decision to leave the show and that Rick was actually Put on a Bus to Hell, making his return pointless now that Uncle Jack showed up.