The production company Vanity Plate at the end of shows produced by Chuck Lorre (Dharma and Greg, Two and a Half Men, The Big Bang Theory) contains text written by him. The text can usually only be read by freeze-framing on it (using a VCR or DVR). The card is different for most episodes and is numbered, starting with #1 for the first episode of Dharma & Greg and continuing through the other shows.
In ESPN's Around The Horn, frequent panelist Woody Paige appears with a chalkboard on the wall, with a new saying (typically humorous, sometimes snarky) appearing after each commercial break (as long as he isn't eliminated from the game)
The opening credits includes the current population of the Rag-Tag Fleet. This tally is updated in each episode, based on the events (and body count) in the previous episode (and the teaser, if someone dies before the opening credits).
Each episode of Blackadder II has a humorous summary of the episode's plot as lyrics for the closing theme song sung by a minstrel fleeing the wrath of the title character. In one episode, he finally catches the minstrel and beats him. In another, the minstrel unexpectedly bonks Edmund over the head with his lute and dances round the unconscious figure.
Also, the opening credits end with a hand placing some object on a table. Each time, the object pertains to that episode's title.
Starting with the 2007 season, The Chaser's War on Everything features an image of a celebrity with a caption underneath it which is different in every episode. Also, a number of the "locked on" images in the rest of the title sequence are different in each episode.
There's an opening sequence where Colbert is in a box filled with patriotic words (and an eagle?). The Couch Gag, which doesn't change every episode but rather once every couple of months, is the last of a certain flurry of words. It's often a nonword, such as "Megamerican", a short phrase, such as "George Bush have a hotdog with me!", or both, in the case of "Factose intolerant". Leading up to the election, it was simply a command to "Vote".
Almost every episode opens with Stephen giving a humorously-worded description of the topics he'll be covering (accompanied by punny captions) followed by a non-sequiter one-liner right before the credits.
Episodes of Conan that debuted on Thursdays usually have a different variant of the "bridge scene" which varies from week to week, such as:
Ones done in the style of a movie or TV show (Such as a "Back To The Future" version where the car travels through time)
Ones based on current events (One that aired on the opening day of baseball season had a variant where the car drives to a baseball game a and baseball flies into the camera)
Ones just plain different than usual (Such as the car being replaced with a clown car that overstuffed the house, robotic legs sprouting from the house and walking away, or the Dreamworks kid in the moon hooking the car by accident).
During a week of shows filmed in New York City, each episode featured the same gag: The family jumps onto the top of an underground subway.
In some cases, the show's opening credits also look different (The aforementioned New York City episodes were done in the style of a subway map and there was also an episode opening done as the opening to Happy Days).
Guest names on the title cards are usually accompanied by icons demonstrating the medium of whatever they're promoting (the typical ones being a TV for a TV actor, a reel-to-reel projector for film, a microphone for comedians, and music notes for musicians). Occasionally, guests have icons specific to them (such as "Nerdist" podcast host Chris Hardwick's name being accompanied by the Nerdist symbol◊).
In another example, after Conan walks onstage and points to Andy Richter, Andy often employs some sort of improvised visual gag that changes from episode to episode, such as pulling a weird face, making use of a prop, standing at an odd angle relative to the camera, etc.
Has a literal couch gag during The Tag. Save for the first and eighth episodes thusfar, every show will end with Abed and Troy (many times literally on the couch in the library) doing/saying something funny, right before or as the credits begin to roll.
As of the second season, certain special episodes have new versions of the title sequence. The Halloween episode (paid out of the creator's pocket) altered the scribbles on the cootie catcher and desk to fit a scary theme, the animated Christmas episode had Abed sing new lyrics to the theme song while dancing on the cars in the parking lot, and the Dungeons and Dragons episode changed the scribbles and theme song to medieval versions.
On the second season, the "Welcome To" part of the title sequence was changed to a gag subtitle lampshading the fact that the title no longer goes with the premise but the producers coudn't find a better one. For example, the season opener reads "Still Cougartown", while a later episode has "Titles are hard".
A season 3 episode even references the Trope Namer: "This is not The Simpsons chalkboard thing. This is not The Simpsons chalkboard thing. This is not The Simpsons chalkboard thing."
Cult has split-second shots of images from later in the episode on each title card.
Episodes on the set of created in 2007 open with a shot of a globe with a scrolling marquee on it. The marquee displays a list of cities that changes each episode, often following a theme (such as ancient cities, cities with "Sioux" in the name, etc.).
"And here it is, your Moment of Zen." Every episode since the show's creation has had a "Moment of Zen" Stinger clip tagged on to the end — except the first episode after 9/11, when the Moment of Zen was Jon Stewart holding a puppy.
Chris Morris would conclude all but one episode by reading tomorrow's tabloid headlines, i.e. "Lord Mayor's Pirouette in Fire Chief Wife Decapitation."
Episodes ended with the camera panning out on Chris and the studio lights dimming, Chris would use this opportunity to perform an assortment of bizarre activities during the credits, such as stealing all the pens around his news desk, shooting heroin, and removing a wig revealing long, blond hair. The last episode concluded with Chris lying on the ground in front of his news desk as if he were worshiping it.
On occasion, the music track playing over the credits would skip like a broken record near the end.
Episode 5, which featured Chris inciting a war between Australia and Hong Kong, concluded after the credits with a rather humorous advertisement for a home video series on the war covered during the episode.
The Dick Van Dyke Show has different openings where he either tripped over the footrest, then later lampshaded it by stepping around it. And there's also a rarer third version that has him step around the footrest, only to trip slightly on the rug as he greets Buddy.
The production company for Everybody Loves Raymond, Where's Lunch. In their vanity plate, the company logo is printed on a table, and then covered up as a waiter serves a plate of food, which is different every episode. For the last episode, the waiter delivers the check: "No Charge, Thanks!"
In the third season of Australian sketch show Fast Forward, a VHS disclaimer would scroll up really quickly, followed by "Ah good. You've paused the tape. Welcome now to FREEZEFRAME THEATRE." The script for a soap opera style scene would scroll quickly, followed by the rest of the disclaimer.
Fawlty Towers includes a hotel sign in the opening credits. This usually either has letters missing or is rearranged into anagrams or partial anagrams of itself, like "Watery Fowls", "Flay Otters", "Fatty Owls" and "Flowery Twats".
Flash Forward has split-second shots of images from later in the episode on each title card.
The show's opening title is shown in a different color each season, and the accompanying animation of the Seattle skyline ends with a number of different variants. Some of the various animations:
Fireworks shoot over Seattle.
A hot air balloon flies over Seattle.
The sun rises over Seattle.
The moon rises over Seattle.
A stylized raincloud is shown.
A stylized thundercloud is shown.
A shooting star streaks across the sky.
Lights come on in the building windows.
A plane towing a KACL advertising banner flies across.
An elevator travels up the Space Needle.
A helicopter appears from the back of a building near the Space Needle.
A rainbow appears over Seattle.
The Space Needle is strung with twinkling Christmas lights.
As Kelsey Grammer sings the closing theme, he throws in an interjection after the first line: "Mercy!", "Quite stylish!", or "Oh my!" He adds another one at the end: "Thank you!", "Good night!", "Good night, everybody!", "Good night, Seattle, we love you!", or "Frasier has left the building!" Sometimes the theme extends a little bit as he also throws in the line "Scrambled eggs all over my face! What is a boy to do?"
At the end of the episode where the station manager decides to switch KACL to "all Latino music, all the time!", the Theme Tune is changed to a Latino version, with lyrics in Spanish.
The credits to each episode of Game of Thrones feature a pop-up book style map of the major areas of importance to the episode. These locations change gradually with each episode (though some remain common throughout). Occasionally results in a Spoiler Opening scenario as the sudden presence of an unfamiliar location in the credits serves to telegraph that the series is moving into a new region in the upcoming episode.
In Green Acres, after the opening title it's usually Lisa Douglas who would notice "It's time to wake up and see the names!" or some other variation.
Grounded For Life contains a couch gag of a musical variety as the riff which closes the show's opening theme is slightly different in each episode.
The first version of the Hangin' with Mr. Cooper opening has the title character saying something different before and after the theme song. This was also something that had several versions as opposed to being different every time. The second changes his set of after-song quips.
The opening to the British sketch show KYTV changed from episode to episode based on whatever "show" was being broadcast.
The opening sequence to the post-apocalyptic show Jericho always featured a telegraph beeping in the background. If one knew Morse code well enough, one could tell that each episode's plot was given away by the message ("There is a fire" the week half the town burns down, etc.).
The last card of the opening credits montage on Last Week Tonight with John Oliver has a reference to one of the previous week's events (for example, the card on the episode that aired after the 30th anniversary of Watergate was of President Richard Nixon.)
The last segment to each episode of The Late Late Show With Craig Ferguson begins with the title card "What did we learn on the show tonight, Craig?" with a kitten. What happens next changes from show to show, and it's possible to see a full month of episodes without seeing the same thing twice.
Late Show with David Letterman
Announcer Alan Kalter gives David Letterman a different intro on every episode. A carry-over from when Bill Wendel was the announcer when Letterman was on NBC.
The title sequence also used to begin with "From New York <gag describing the city here>, it's Late Night/The Late Show with David Letterman!"
Match Game: Host Gene Rayburn made a different entrance for each show. Once, this involved him breaking down the doors.
The opening credits for the original Mission: Impossible included a montage of short clips taken from the episode itself.
While not exactly a "gag", during the theme song of every episode of Mister Rogers' Neighborhood, Mr. Rogers would put on a different colored sweater. Obviously there were duplicates considering how long the show ran.
Except for the short fourth season, the show use thematic gags to introduce the opening titles. In the first season, Michael Palin, dressed as a hermit, runs up to the camera and says, "It's..." In the second season, John Cleese appears seated at a desk and says, "And now for something completely different," followed by a shot of Palin saying "It's..." In the third season, a nude Terry Jones plays an organ chord, followed by Cleese's "And now..." and Palin's "It's..."
Subverted in the Second Season when, in one episode, Cleese does not appear before the opening titles. After the opening titles, Cleese appears sat at a desk and says, "You probably noticed that I didn't say 'And now for something completely different' this week. That's because I'm unable to appear in this week's show..." before looking in dismay at his script.
The beginning of every episode of Mr. Show has someone say (or a variation of) "Hey everyone! It's Bob and David!" For the first two seasons, it's Mary Lynn Rajskub so it's only this trope depending on what or how she says it. In the third and fourth season (after Rajskub left), it's one of the cast members, typically as a character they play within the episode.
In the second season of Dawn French's Murder Most Horrid, the second-to-last line of the theme song would be different in every episode; they would all rhyme with "horrid." (sort of)
The show had a "stinger" — a five-second clip from that day's movie, usually something that would be bizarre even in context — after the ending credits. As well, some episodes had different music or spoken lines over the end credits.
For the Hamlet episode, the entire ending theme was replaced by the audio for part of the "to be or not to be" monologue (in keeping with the final scene, in which Tom and Crow present Mike with a talking Hamlet action figure).
Many episodes in the second half of season 5 (i.e. after Mike replaced Joel) had alternate Eye Catches showing something odd being thrown at a blackboard.
In each episode of NUMB3RS, the action is preceded by a four-quadrant grid, each quadrant of which contains a number of something — suspects, dollars, crimes committed per day, people, whatever — relevant to that episode's case.
Once Upon a Time has a different fairytale character, creature or item appear in each episode's title card.
Person of Interest: Right at the end of Finch's narration during the full-length opening sequence ("Victim or perpetrator, if you're number's up, we'll find you"), the person of interest for that episode is shown, in a shot from later in the episode (like the FlashForward example above, but it lingers for a couple of seconds), usually with Reese following them as well.
Please Like Me: every episode starts with the protagonist (or, in one case, his mother) preparing some kind of food — generally whatever is mentioned in the episode's title.
Each episode ends with the characters frozen in mid-laugh in traditional style while the credits rolled, but rather than freeze the image, the actors would just remain still. Each episode played with this in a different way, such as having the recently-arrested perp notice that everyone else has frozen, and escape, or having one character in the middle of pouring coffee, resulting in it overflowing from the cup.
Likewise, in the opening titles, the "special guest star" would be introduced ... and then killed off during the title sequence.
It's very subtle, but almost every episode of The Prisoner uses a different mix of the opening Theme Tune: the section accompanying the scene where the future Number 6 confronts his boss is remixed to emphasize different instruments. Each episode is also supposed to begin with a version of the same dialogue between Number 6 and Number 2, with the voice of Number 2 changing in each episode. However, in some episodes the actor playing Number 2 did not record the lines, or the identity of Number 2 was hidden, and so a generic voice was used instead.
In the first two seasons of Red Dwarf, each episode would begin with a "Distress Call" in which Holly, the ship's computer, described the ship's situation (and the show's premise) and then finished off with a humorous remark (different each episode) about the situation, recent events, or the crew's hopes for the future. One of these was even used as a retroactive Reset Button: The most important event that happened recently is that Lister pretended to pass a test to be a chef, when in fact he failed. "That should tell you something about how interesting things are here."
The original opening Sabrina the Teenage Witch would have Sabrina changing into 4 different outfits in front of her mirror, the fourth always being different. She would then make a quick pun or observation.
The Sarah Silverman Program always has an opening where Sarah gives a run down of the characters on the show while showing pictures (some completely random), but the pictures she shows and what she says is different for every episode.
The Seinfeld logo is always a different color every single episode.
The ending to the opening of Shake It Up has Rocky and CeCe in different outfits — this, however changes every season, not every episode.
Each episode of Six Feet Under opens with someone else dying in some absurd way. It is a show about a funeral home, after all.
Not quite a proper Couch Gag, but perhaps something of a prototype: the "family photo" scene at the end of the opening credits to Soap alternated between several different versions.
The Soup has its own literal Couch Gag: during the opening sequence Joel and the dog can be seen on a couch watching a clip from/relating to a big media event of the previous week.
Spencer: The short-lived NBC teen sitcom featured the title character (Chad Lowe) pulling a different classroom prank — often, quite elaborate — before being sent to the principal's office. The opening credits then showed Spencer walking down the hallway to the principal's office.
On USA Network's game show Strip Poker, hostess Jennifer Cole always had a different explanation for why the deuces through eights were omitted.
The closing shot of Tosh.0 changed from "season" to "season". Originally, it was just a wide shot of Daniel, the green screen, and the audience. Later on, various actions were added in, such as the audience pelting dodgeballs at Daniel. They currently have the same basis per "season", archived for posterity:
Winter 2011: Daniel walks across a catwalk.
Summer 2012: A random audience member stands up and shouts something random at Daniel (such as "I took a s*** in your cereal!").
Fall 2012: A close up of a body part flashes on screen for half a second.
The show changes their Operators Are Standing By introduction clip each episode, where the operator woman and her headset do something stupid like try to answer a phone upside down, or nearly choke to death on the headset cord.
Starting in season 3 following the format change, after the opening Chris Hardwick (the host) would run down the hall to the studio and encounter or do something different. Such as being chased by a mob (who would back off when they realize they were entering a area where they're taping) or using the Portal gun. Likewise the "Firsties" segment the announcer would often change the way how he shouted it.
At the beginning host Clive Anderson started out introducing the players and their showbiz origins, then got bored with that and switched to more original, thematic introductions, with a theme and usually a sting for the fourth one.
Clive: The greatest thing from America since sliced hamburgers, Mike McShane; and the most interesting Canadian after the maple leaf, Colin Mochrie; and the biggest thing in show business since Barnum and Bailey's tent pole, Ryan Stiles; and finally the most interesting thing to come out of Gunnersbury since the North Circular Road, Tony Slattery.
Drew introduced each episode's contestants by using slogans, figures of speech, or other popular phrases while replacing the last words of the phrase with the contestant's name.
Drew: If at first you don't succeed, try Greg Proops! If you can't stand the heat, get out of the Wayne Brady! If you don't have anything nice to say, don't say Colin Mochrie! And if you think you have problems, Ryan Stiles!
Ryan's habit of making a funny expression into the camera during the intro can be traced back to the last UK season. In the US version, all four of them will be making an odd face for their introduction.
Drew: "Welcome to Whose Line is it Anyway?, the show where everything's made up and the points don't matter. That's right, the points don't matter, just like [humorously irrelevant thing]."
The final game of the British series, probably counts as a Couch Gag: The Winner or Winners of the show read the credits in the style of Clive's Choosing.
The American version started without this aspect, then eventually added it after a few seasons.
Xena: Warrior Princess and Hercules The Legendary Journeys have a bit right near the end of the credits that riffed on the standard No Animals Were Harmed disclaimer, usually a comedic bit referring to the events of the episode. For instance, during the "Hope" arc which set Xena and Gabrielle against each other, one of the episodes made the comment that "Xena and Gabrielle's relationship was harmed during the filming of this episode."