Doctor Who had two films starring Peter Cushing as 'Dr. Who' which took place outside the series' continuity. "The Five Doctors", a 90-minute special to celebrate the 20th anniversary, was basically a Movie. Another film was the 1996 Paul McGann TV movie, which was an attempt to get the show back on track after its original 1989 cancelling. The 50th anniversary special was billed as a movie, and showed in theaters along with the global simulcast.
Firefly spawned a theatrical film, Serenity, which tied up most (but not all) of the dangling threads from the short-lived series. Universally known to fandom as the Big Damn Movie. Fan Fiction even uses this to help identify the time frame: Post Show Pre BDM, Post BDM, No BDM. There are some that are Post BDM + AU.
Blue Mountain State ended after 3 seasons. While the final episode did finish its story, fans wanted there to be at least one more season (students normally spend 4-6 years in an American college and since each season represented a school year, fans wanted to see Alex Moran's senior year) to the point where they signed a petition and the creators launched a Kickstarter. The result was Blue Mountain State: The Rise of Thadland, released on February 2, 2016.
This was also the case for the original Battlestar Galactica, at least in Canada and Europe.
...and In America! Where it appeared in some theaters ... in Sensurround!
Mystery Science Theater 3000 's movie was actually shorter than any episode of the TV series - having apparently had a few of the 'host segments' cut right out just prior to release - and featured slightly dumbed-down riffing (i.e. fewer obscure references, more crude language) as well as an actually tolerable movie (This Island Earth, considered by many to be a sci-fi classic) due to Executive Meddling. This is not to say the movie isn't still pretty funny.
This Island Earth was itself edited down significantly for use in the MST3K movie which- even including the new footage- still ran almost 15 minutes shorter than the original film.
Star Trek and Star Trek: The Next Generation have had 10 films between them — six of the former and four of the latter. In a more conventional way of speaking, however, the first one (Star Trek: The Motion Picture) was the Movie for TOS and the seventh and first unnumbered one (Star Trek: Generations) for TNG—the sequels to them essentially icing on the Movie cake, allowing their respective shows to basically continue well past their final TV episodes and to engage in the Grand Finales they didn't have during their original run. Then again, if you have not heard about the "even-odd rule"... basically, there is a strange pattern in which the even-numbered films are (in general) better than the odd-numbered films. The result is that the second TOS film, The Wrath of Khan, is usually considered their best, and the second TNG film (movie #8), First Contact, is also considered the quintessential TNG film, distilling all that was best in their respective series. Still, their first movie outings still had that "The Movie" effect, where everything was a shiny new movie set focusing more on "wow, we're actually in a theatrical film now". Of course, of the four TNG films - movies #7 through #10 - #7 and #9 fell victim to the odd-numbered rule (though #9 is more like a pleasant stand-alone, the cast officially thinks it's boring), and #10 (Nemesis) officially broke the "even numbered Trek films are great" rule (the cast openly stated that "it sucked"), First Contact was the only TNG film widely accepted as a great entry.
Reviews for The Motion(less) Picture were better than one might expect based on how commonly it's panned today (Ebert gave it 3/4 stars, and it's got a 45% on Rotten Tomatoes, which is ... well ... rotten by the stated standards, but significantly higher than a lot of arguably better movies). While it didn't meet its over-optimistic revenue expectations, it did at least make back its budget 2-3 times over, which was good enough for Paramount to green-light a (lower-budget) sequel after booting Roddenberry, who was perceived to be much of what went wrong with the first one.
Also - according to Adam West, the third season's three-part arcs were meant to be edited together into telefilms for overseas distribution (as with several contemporary shows like The Man from U.N.C.L.E.. It's unknown if any of these plans actually went ahead, though.
McHale's Navy spawned two movies during its run as a TV series in the early 1960s; then The Film of the Series in 1997 attempted to tell an "after-the-series" story mainly by ignoring the show's World War II roots and throwing in a Cold WarRetcon.
Rescue From Gilligan's Island had the cast finally escape the island, struggle to reintegrate into normal life, and finally become shipwrecked on the island once again during a reunion cruise.
The Castaways on Gilligan's Island saw them escape yet again, but return to open a holiday resort. This was intended to be the pilot for a Spin-Off that never happened.
The Harlem Globetrotters on Gilligan's Island saw, you guessed it, The Harlem Globetrotters crash landing on the island before helping to thwart the schemes of a Mad Scientist who wants the island for its rich energy supply. The issue is, naturally, settled in a basketball match between The Globetrotters and the Mad Scientist's robotic team.
Noah's Arc: Jumping the Broom, the movie about Wade and Noah's wedding (and the craziness that precedes it).
After already being a spinoff of the original Stargate movie, once Stargate SG-1 was canceled, the major plot of the ninth and tenth seasons was brought to a climax in the movie Stargate: Stargate: The Ark of Truth. This was then followed by a sequel called Stargate: Continuum. Further movies were apparently planned, including another SG-1 movie, an SGA movie, and an SGU movie, but these have since devolved into Development Hell if not cancelled altogether.
The unusual thing about Stargate fandom is that the film referred to as "The Movie" is actually notThe Movie in the sense of this trope; it was the first film that everything else is based on (essentially the opposite of The Movie). The reason for this is simply that it's the only part of the entire franchise that doesn't have a subtitle, so there's pretty much nothing else to call it. And then it gets even more complicated because the cast and creators of the film don't consider the series canon, and have frequently remarked on their desire to complete the film series as they intended and ignoring the spinoff entirely, while the series in turn diverges from the movie in a number of areas as well.
So while other shows might have The Series followed by the Big Damn Movie, Stargate has The Movie followed by the Big Damn Series. (This is considering that in the first movie they only saved one planet, whereas afterwards they go on to save multiple galaxies several times over and uncover the Secrets of the Universe).
Numerous Brit Coms of the 1970s had movie spinoffs, featuring the original cast and (usually) writers, but filmed on different sets and locations. These films typically featured the cast going on a bus trip, or a cheap foreign holiday, and generally had poor reviews. Examples include:
It's worth recording Nick Hornby's reaction to these things, when he was watching them as a kid. 'For me, growing up, the cinemas wasn't a place of magic and wonder. It was where old sitcoms went to die.'
While Fawlty Towers never actually made The Movie, John Cleese did consider doing one at some point. The idea he came up with plays with the whole Vacation Episode plot in that it apparently involved Basil Fawlty trying to go on holiday to Spain, only for the plane to get hijacked and forced back to London — which ended up driving Fawlty so crazy that he ended up hijacking the plane himself just to get his holiday.
Thunderbirds: The series was followed by two theatrical movies, which were unexpected box-office flops (in fact, the second film was greenlighted despite the first one being a flop as they thought it was a fluke!).
In one of the largest dichotomies in this trope, the otherwise-cheery and humorous Sesame Street had Follow That Bird, a full-length Tear Jerker of a film that delves into much darker territory of family, loss, and self-identity than anything that ever showed up in the normal show. This was followed over a decade later by Elmo in Grouchland.
Family Ties Vacation sends the cast to Merrie Olde England after Alex wins a summer scholarship to Oxford.
The Facts of Life had more than one of these: The Facts of Life Goes to Paris sends Mrs. Garrett and the girls to France, while The Facts of Life Down Under sends them to Australia. There was also a reunion movie about a decade after the show ended.
Moving into the '90s, Sabrina the Teenage Witch had two during the run of the live-action show: Sabrina Goes To Rome and Sabrina Down Under. Unlike most movies of this ilk, the majority of the regular cast weren't involved (in both cases only Sabrina and Salem got to make the trip).
Leave It to Beaver had a reunion movie (Still the Beaver) which led to a new series (titled, creatively enough, The New Leave It To Beaver) in the '80s. It also had a very forgettable theatrical version, with a whole new cast and set in more modern times, in 1997.
The Brady Bunch had two reunion movies The Brady Girls Get Married, A Very Brady Christmas. Each of these spawned a short-lived series (The Brady Brides, The Bradys).
The Ultra Series has done a fair number in its later years.
In 1990, Ultra Q got one (some twenty-four years late!) called Ultra Q The Movie: Legend of the Stars, featuring an alien named Wadatsujin and her kaiju Nagira.
Ultraman Tiga: The Final Odyssey was released in 2000 (three years after the series ended), but wrapped up some of the remaining plot points in the series (such as Daigo and Rena finally getting engaged) and featured cameos from the cast of Sequel SeriesUltraman Dyna to bridge the gap between series. It also revealed a fair bit about Ultraman Tiga's past and that of the prehistoric civilization he defended.
Ultraman Cosmos had an entire trilogy. It's first movie served as a prequel to the series and a Milestone Celebration for the franchise's 35th anniversary. The next two movies took place after the events of the show and featured a new hero called Ultraman Justice.
Power Rangers got two movies during the height of their popularity. The first is a non-canon film based on Mighty Morphin Power Rangers: The Movie. It introduced early the ninja powers they would be using for Season 3 (which later formed their own story arc on how they got those powers). The second was used to introduce the Power Rangers Turbo series. This one was part of the TV show's continuity.
On the Japanese end of things, every year (since the early 2000s) there's a Super Sentai/Kamen Rider double-feature (aka Super Hero Time: The Movie (insert year here)), with the Sentai movie getting about half the screen time the Rider movies get. (In contrast to America, where toku shows can be divided into the categories of "Power Rangers" and "everyone else", Kamen Rider is much bigger than Super Sentai in Japan.)
Super Sentai also has a team-up with the current team and its predecessor every January. Kamen Rider is getting in on the action with that lately every December. And now, Rider/Sentai teamups (Super Hero Taisen series) are also going to be an every year thing. So by now, you've got a Super Hero Time double-feature, a Sentai 'versus' movie, a Kamen Rider 'Movie Wars' movie, and a Super Hero Taisen movie every year. Also, if a series is popular enough, it'll get a movie or two after its run finishes, though usually DVD only. Japan really loves its Toku.
Columbo started as an NBC made-for-TV-movie, then spawned a TV series, then spawned even more TV Movies!
Sex and the City took 4 years to get the movie out. Originally planned for the year after, but Kim Cattrall wanted more money for the work. (and who can blame her?) So it dragged on for a while until Kim got a deal.
British political satire The Thick of It spawned In the Loop, in which the action transferred to the US and most of the actors played different characters.
Get Smart had planned to make a full-length movie, which instead became the three-episode story arc "A Man Called Smart". Way after the series ended, there was a bad movie, a made-for-tv movie, and another 2008 movie.
Monty Python refilmed a bunch of their TV sketches and released it in 1972 as And Now For Something Completely Different. It became must-see viewing on the midnight movie circuit.
Our Miss Brooks had a theatrical movie at the end of its run. Miss Brooks finally marries Love Interest Mr. Boynton. She also spends much of her time tutoring a Lonely Rich Kid
Studio 3'sBitcom segment of shorts became popular enough to get its own 40-minute Spin-Off special, Bitcom And The Oblivion Ray.
Barney & Friends had Barney's Great Adventure, a movie where Barney and the kids have to chase after a rainbow-striped egg which contains a creature that can make people's dreams appear before them.
There was going to be a Teletubbies movie, but there was a dispute between the American distributor of the Teletubbies and the original creator of the Teletubbies, Anne Wood. This resulted in the Oogieloves.
Little House on the Prairie had quite a few TV-movies after the series' run which gave the show closure, the most notable movie being when the town of Walnut Grove is destroyed.
A theatrical version of Dragnet was released in 1954. It's slightly Darker and Edgier than the series tended to be, with a bit of a downer ending involving a Pyrrhic Victory. It was notable in being the first movie based on a TV show.
The 1987 theatrical version of Dragnet, on the other hand was pure Affectionate Parody.
The Peter Gunn movie Gunn (1967) had Craig Stevens once again as the title character.
Tracker (2001) had a movie of sorts that was really a couple of episodes edited together and released as Alien Tracker. The poor quality and fan refusal to buy it is probably what made Lion's Gate think DVDs wouldn't sell, and no season set was ever released.
The Muppet Movie and its seven theatrical follow-ups, as well as two TV flicks and a direct-to-video movie.
Blackadder Back & Forth, which had an extremely limited theatrical release; it was commissioned for the Millennium Dome's Skyscape Cinema, and subsequently went to DVD.
Due to the popularity of Flemish series Kabouter Plop created by Studio100, a couple of movies were released in Belgium starting in the mid 2000's.
Downton Abbey ended in 2015, but in 2019 got a full-length theatrical continuation film appropriately titled, Downton Abbey. A sequel came out three years later in 2022 subtitled ‘A New Era’ which serves as the Grand Finale.
The Army Game: 1958's I Only Arsked!, directed by Montgomery Tully and made by Hammer Films. In it, slapstick ensues when the inept army recruits from Hut 29 are transferred to a post in the Middle East.
Miss Fisher's Murder Mysteries received a feature film in 2020 titled Miss Fisher and the Crypt of Tears. In it, Phryne goes on a globetrotting adventure from Palestine to England and back again, dragging a reluctant DI Jack Robinson in her wake. Most of the other series regulars have at least a cameo.
Psych has had two movies so far, Psych: The Movie in 2017 and Psych 2: Lassie Come Home in 2020.
The French Arthurian Legend-inspired comedy series Kaamelott ended in 2009. Twelve years later, the theatrical film Kaamelott: Premier Volet continued the story, and it is intended to spawn a trilogy.
... basically, there is a strange pattern in which the even-numbered films are (in general) better than the odd-numbered films. The result is that the second TOS film, The Wrath of Khan, is usually considered their best, and the second TNG film (movie #8), First Contact, is also considered the quintessential TNG film, distilling all that was best in their respective series. Still, their first movie outings still had that "The Movie" effect, where everything was a shiny new movie set focusing more on "wow, we're actually in a theatrical film now". Of course, of the four TNG films - movies #7 through #10 - #7 and #9 fell victim to the odd-numbered rule (though #9 is more like a pleasant stand-alone, the cast officially thinks it's boring), and #10 (Nemesis) officially broke the "even numbered Trek films are great" rule (the cast openly stated that "it sucked"), First Contact was the only TNG film widely accepted as a great entry.