Albion: Not quite at first sight, but still instant. When Mellthas and Sira discover their ability to communicate with each other telepathically very shortly after first meeting, they see the depths of each other's souls or something and fall in love immediately.
In the Assassin's Creed series, Altaïr does so with Maria, a Christian woman who pretended to be his real target, Robert de Sable. Despite killing dozens of guards just to get to the fake Sable, Altaïr immediately and instantly spares Maria's life, leading, as we learn in the sequel, to Desmond Miles, the main protagonist in the series.
Invoked and defied in Chains of Satinav. When Geron sees Nuri for the first time, he's speechless. Nuri promptly asks if he's in love, and Geron immediately denies it. They're the Official Couple, naturally.
Much to Taiga's dismay in Duel Savior Destiny, Nanashi falls in love with him at first sight due to him being a warm, open person. Why is the sex maniac dismayed at having a cute girl in love with him? Well, it probably has to do with her being undead enough that her limbs sort of fall off at a strong impact.
In Fable I, having a high enough attractiveness and a good enough reputation means that the Hero can't walk down the street without a few nearby men and women hopefully saying, "A wedding ring would be nice..."
Kunihiko Asou and Ouse Kurosawa fell in love with each other the moment they met, but nothing came of it because the former was a guest who left shortly thereafter while the latter was chosen to be a Human Sacrifice.
A more terrifying example involves a photograph of Ouse Kurosawa. Some of the men, upon seeing it, become smitten with Ouse and make their way to marry her, only to be killed off when said marriage goes awry (she's a hostile ghost, after all).
The Feel the Magic series is something of a celebration of this trope, as they both involve your nameless protagonist falling head over heels for a girl and subsequently doing everything he can to win her heart.
It's very obvious that this happened between Sigurd and Deirdre in Fire Emblem: Genealogy of the Holy War, since they are quite clearly attracted to each other when they first meet and later get married in the same chapter they meet.
Strongly implied to be the case with a Male Avatar and Azura; they quickly grow close after their first meeting, have a very fast support growth rate, and she tells him that she's been in love with him for a long time if they get married on the Revelation route.
It can also happen between the Male Avatar and Princess Camilla, as in their S-Support she tells him that she's liked him ever since she first met him.
In the case of a Female Avatar and Silas, the trope is deconstructed because he doesn't exactly believe in this trope... and that's the exact reason why, if he's romanced, it takes him so long to actually realize that it is the case for him in regards to her. And then it takes him even longer to confess because he knows that it sounds like something out of a child's fairy tale, and was afraid of not being taken seriously. This is also lampshaded by their daughter, Sophie, in her conversation with the Female Avatar during the Festival of Bonds DLC.
A man in Grow Island will fall in love with a woman the moment he see her, she return the feelings if he can give her flowers.
In Grow Maze, two hungry creatures will kiss when they notice each others after you put them in the same room.
Possibly occurs with the player and Silk Fox/Sun Lianin Jade Empire. Their first conversation after she joins the party can end with her commenting that their flirting has gone much further than she originally intended and breaking off abruptly.
Shown in a cutscene of Jak II: Renegade, where Jak falls for the Girl Behind the Curtain upon meeting her, and is stunned by love at the end, with Daxter franticly trying to snap him back into reality. The girl turned out to be his Love Interest Keira Hagai, whom he had not seen for two years.
Seeing as King's Quest is based on fairy tales, this trope gets thrown around liberally. In the Back Story, this happened for King Edward the Benevolent, and it turned out badly (she was a witch scheming to get the magic chest of gold). Graham gets hit with this himself when he sees Valanice imprisoned in Kolyma, and his son gets a dose when he meetsPrincess Cassima. The exception to the rule, like usual, seems to be Rosella. While Edgar got a case of this upon seeing her in King's Quest IV, it took her a while to share the opinion.
The female variant can start shamelessly flirting with Carth straightaway, too. He kinda likes the attention...well, until his paranoia kicks in. The Gay Option can also proceed like this, with lines like "Juhani, you are a beautiful woman with so much talent." Courtnay Taylor's voice acting wrecks any attempt to keep it at subtext.
Knights of the Old Republic II: In the cut content, given high enough Relationship Values, after loses his fight against Darth Sion, Atton tells the female Exile in his dying moments that he loved her from the moment he met her and tried to play it off as a joke.
The Last Sovereign: In the prologue, Altina proclaims her undying love for the Chosen One Kai. They've known each other for less than an hour at this point. Riala, the succubus who is about to kill Kai, is not impressed.
Riala: I'm literally an evil incarnation of sex and I know more about love than you.
In Left 4 Dead 2'sThe Passing, Ellis instantly falls in love with Zoey the second he sees her. Even saying they will skip the dating part and get right to the marriage. Well considering it is the Zombie Apocalypse, there probably wasn't time to date anyway.
In the The Legend of Zelda franchise, this is implied to be a recurring thing between the various incarnations of Link and Zelda. One moment that stands out is early in Hyrule Warriors; Zelda is walking along the battlements while Hyrulean soldiers-in-training are sparring. Link happens to look up as she's looking down. Nothing is said; nothing needs to be.
Paya in The Legend of Zelda: Breath of the Wild. From the moment Link appeared on her doorstep, she never understands why his appearance and heroics won't stop running through her mind. She even dreams about Link during the limited amount of sleep she finds.
Life Is Strange: Before the Storm: The morning after Rachel and Chloe meet at the Mill, Rachel drags Chloe into Drama club to give her opinion on the supposed Love at First Sight between Miranda and Ferdinand in The Tempest. Subtext makes it clear that she's also talking about herself and Chloe. Chloe can either dismiss it as stupid kids who don't know any better or something real. Of course, since it's Rachel, it's hard to say if she actually believes it or is just trying to manipulate Chloe. For what it's worth, with high enough Relationship Values Rachel spends pretty much the entire rest of the game trying to prove that her love for Chloe is real.
Averted in Magiulovestruckm, as while Barry is physically attracted by Rose at first sight, choosing to have him declare love for her in chapter 6 will result in her not taking you seriously, since you've only just met. Even if you just decide to tell her that Barry was stunned by her beauty, he makes it clear that he doesn't plan on starting a relationship before taking the time to know her. Rose herself will only start to have some feelings for Barry after witnessing him take on Tyrath.
Though Neeshka admits later on that the player was the first person to be nice to her. It's understandable that she'd latch on to him.
In Odin Sphere Oswald the emotionless Shadow Knight fell in Love at First Sight with Odin's daughter Gwendolyn when he saw her wearing her late mother's dress while on a spying mission in Odin's realm. A feather she left behind reminded him of the prophecy of the dragon Hindel: "Seek the bird... that shall be your destiny."
Entirely possible in The Sims 2 if you have the Seasons expansion and earn the Wishing Well reward. If a sim successfully wishes for "true love", another sim (usually a Townie or another playable) with the most compatible traits and personality emerges from the well and greets them for a kiss, which automatically boosts their relationship to 70/70 and raises the "in love" flags.
Downplayed in The Sims 3. Highly compatible sims will not fall in love just by meeting each other, but will express a strong interest in each other to indicate that they can make a very good couple. The player has the option of playing it straight by romancing and starting a relationship on the spot though.
Played straight in Supernatural expansion, where Witches can cast a spell on another Sim that will make them fall in love with the next person they interact with.
In Uncommon Time, Aubrey falls hopelessly in love with Alto the moment they see her. This might have something to do with the fact that she's the first person they see when they're revived from their hibernation spell.
In Valkyrie Profile, Lezard Valeth fell for Lenneth Valkyrie upon first sight. Which resulted in him becoming a creepy, obsessive Stalker with a Crush. Oddly, you never actually get to see just where and how he saw her.
In World of Warcraft, one of the reasons Sargeras the Burning Titan is so determined to conquer Azeroth is because he had a vision of the Titan World-Soul within Azeroth opening an eye to look at him and from that moment on he coveted her for himself.