Official Kiss

Show, Don't Tell is a main rule of all fiction, visual or not, and applies even more so in emotionally-charged moments of triumph and heartwarming that are seen as having a duty to be as vivid and narratively satisfying as possible to make the audience cheer with glee. Since the Relationship Upgrade in successful romance almost always qualifies for this, there's a strong tendency for characters to act out the moment of upgrade with a big, uncomplicated smooch.

Often, especially in Unresolved Sexual Tension (and its cousins Belligerent Sexual Tension and Love Epiphany), this is a couple's very first time kissing each other, but this is not always the case. It is, however, often portrayed as the couple's first "real" kiss, meaning it can be the first romantic kiss between two characters that have previously kissed due to other motives, the kiss that marks the moment when two exes reconcile, when a casual dating situation turns into true love, or when a couple that has made some motions towards romance in the past finally become a real couple.

A major staple of TV shows.

Compare Relationship Upgrade, They Do, Love Epiphany, Love Confession. Almost always a Hollywood Kiss, and when it's not, it's usually a subversion. Frequently a Big Damn Kiss. A common feature of a Cliff Hanger or Season Finale.

WARNING! There are unmarked Spoilers ahead. Beware.

Examples of Official Kiss include:

Anime and Manga

On the very last page of Bakuman｡ Mashiro and Azuki finally have their first kiss.
Fairy Tail: after 200 chapters of beating around the bush when not separated by various circumstances, Erza and Jellal kiss at last! Well, probably... after that Jellal makes up a lie about being already engaged because he doesn't think he has the right to love anyone. Erza doesn't buy it but pretends to. So maybe it doesn't count after all.
In phase 31 of Mobile Suit Gundam SEED, after spending most of the series up to that point in various stages of Unresolved Sexual Tension, Murrue Ramius asks Mu La Flaga what prompted him to come back to the Archangel when he was supposed to be on his way to a new assignment. Mu seems momentarily perplexed by the question, and answers it by kissing her, after which the two of them are officially a couple with not much more needing to be said on the subject.

Film-Animated

Commonplace in the Disney Princess movies. They usually get one kiss right before the big wedding scene.

Film-Live Action

Kaylee and Simon get theirs in the Serenity movie.
Reed and Sue get theirs at the end of the first Fantastic Four movie.
The Sure Thing: In the penultimate scene, Gib finds out that Alison broke up with her fiance and she finds out he hasn't slept with the titular "Sure Thing". Cut to the roof where Gib had taken Alison earlier in the movie. Gib and Alison are kissing. The movie ends here and it is obvious that the two are now together.

Literature

Harry and Ginny, late in Harry Potter and the Half-Blood Prince, Ron and Hermione have theirs during the final battle in Harry Potter and the Deathly Hallows. ("Oi, there's a war on!")
In King Kelson's Bride, Araxie arranges to secretly meet Kelson (they haven't announced their betrothal to avoid offending the Mearan Ramsays) to make a suggestion to solve his thorny problems with his prospective relatives; he's so overjoyed with her brilliant idea he takes her face in his hands and kisses her. They're both a trifle astonished at how much they enjoy it, particularly so early in their arranged relationship.
The Wolves of Mercy Falls, in the third book, Cole and Isabel kiss, for the first time, with meaning behind it. The reader is alerted to the fact that this Kiss meant something more than any other time the two kissed

Live-Action TV

Sam and Diane on Cheers have theirs in the first season finale.
Dave and Maddie of Moonlighting, in "I Am Curious...Maddie".
Ross and Rachel on Friends, in the second-season episode "The One Where Ross Finds Out".
Niles and Daphne on Frasier, in the seventh-season finale. ("Oh, for heaven's sake Doctor Crane...")
Odo and Kira of Star Trek: Deep Space Nine, in the sixth-season episode "His Way". Doubles as a Big Damn Kiss.
Barney and Robin on How I Met Your Mother in the season four finale, in contrast to their earlier comfort-sex making out in season three.
Buffy and Spike on Buffy the Vampire Slayer, in the sixth-season episode "Once More With Feeling".
- Buffy and Riley also have one in "Hush", because they've been literally struck mute and can't express themselves any other way.
- Cordelia and Xander, while they're stuck hiding from a monster made out of maggots, suddenly start making out. After that they're a couple for a while.
Josh and Donna on The West Wing, in the teaser of season seven's "The Cold".
Glee:
- Will and Emma during season 1.
- Kurt and Blaine in season 2.
The X-Files: Mulder and Scully in the end of season 7 episode "Millennium".
Chuck Bartowski and Sarah Walker. Depending on your interpretation, there are two specific points where it happened: either "Chuck Versus the Colonel," when they mark their first Relationship Upgrade, or "Chuck Versus the Other Guy," where they reconcile for good after the Reset Button was hit.
Dollhouse: subverted. When Topher and Bennett kiss, all the signs are there for their Relationship Upgrade. The relationship had been toyed with up to that point and this moment clearly shows that they are an item. And then Bennett drops dead.
The Big Bang Theory: Penny and Leonard had kissed a few times but she was either depressed/drunk or it was a goodnight kiss for a solitary date they had. In the second season finale it was clear she was starting to have romantic feelings for him, but didn't want to interfere with a summer-long expedition the group was going on. When Leonard returned in the third season premiere he could barely get out a "Hi, we're back!" before she jumped into his arms and kissed him.
Merlin: Gwen/Arthur, mid season 4.
Heroes: Peter and Simone under Simone's red Umbrella of Togetherness in "One Giant Leap".
Babylon 5: John Sheridan and Delenn, for the first time in proper time, anyway in "And The Rock Cried Out 'No Hiding Place'". Keep in mind that he had first confessed his love for her nine episodes earlier, but they got interrupted by first Ivanova, and then that pesky war they were both in charge of.

Newspaper Comics

Jon and Liz in this Garfield strip.

Visual Novels

Yarudora series vol.2: Kisetsu o Dakishimete has straight, subverted, and averted examples:
- Played straight with Mayu: the kiss she and the protagonist share at the climax of the game, after the Race For Your Love sequence, is a True Love's Kiss that not only cement their love, but also revives Mayu's memories.
- Subverted with Tomoko: she and the protagonist share their first and crucial kiss mid-way in the game, and the kiss sequence's symbolic animation is similar to Mayu's; but the storyline after this sequence will pit you with several bad choices that can break the Relationship Upgrade and provoke Bad Endings. If you pick the good choices, there will be a second kiss between Tomoko and the protagonist during the climax of the game: that kiss will definitely solidify their relationship, as Tomoko will finally have overcome her Clingy Jealous Girl tendencies.
- Averted with the Sexy Lady: if you try to kiss her, a Yakuza who considers her as his woman will come for a "nice talk", leading you to a Bad Ending; and there will be no other opportunity for a kiss with her in the remainder of the game.

Web Comics

Freefall: Florence and Winston finally have theirs.
The probably most famous page in the fan-made Chip 'n Dale Rescue Rangers graphic novel Of Mice and Mayhem.

Western Animation

Kim and Ron in the Kim Possible movie "So The Drama".
Avatar: The Last Airbender has Sokka and Suki's kiss in "The Serpent's Pass" (Sokka's previous kiss with Yue was a Last Kiss) and Aang and Katara's kiss in the finale (Their previous kisses were either imaginary or instigated solely by Aang.) Zuko and Mai don't have one as they were established as a couple before the Maikouts happened.
Robin and Starfire in the Teen Titans movie "Trouble in Tokyo"
M'ggan and Superboy in the Young Justice episode "Terrors." Previously, the Everyone Can See It quotient had been so high that people who only knew their civilian identities assumed they were dating, yet they were not together. After the kiss, the next we see of the two, they are a couple. No conversation necessary.
Kevin and Gwen in the finale of Ben 10 Alien Force, which also served to celebrate that he'd been cured of his patchwork monstrosity condition.
Candace and Jeremy get theirs in Phineas and Ferb: Summer Belongs To You
Fry and Leela at the end of Into The Wild Green Yonder in Futurama.
Eddy and Nazz at the end of Ed, Edd 'n' Eddy's Big Picture Show.
- There's also Eddy and Edd in "Your Ed Here", but that was just because Eddy thought Kevin was telling Nazz his middle name.

Real Life

Ceremonial kisses at weddings.