Fully Functional: Any episode with Data & Lore or their "father" Dr. Noonien Soong. (Also see the episode " Brothers" which was Acting For Three (including one stint in enough make up to make a Klingon's actor cry.) And let's not forget "A Fistful of Datas", where Data plays...a fistful of ancient Western stock-characters.
"The High Ground" got banned from broadcast in both the UK and the Republic of Ireland due to a line about Ireland being reunited in 2024 following a successful "terrorist" campaign.
Contrary to popular belief, "Conspiracy" was never banned in the U.K. It aired on the BBC at 6pm as normal, but was very heavily edited: the scene actually ends with Riker and Picard firing their phasers at Remmick off-screen. The episode was not aired uncut in the U.K. until a few years later when Sky showed it after the 9pm watershed. However, the "exploding Remmick" scene was accidentally left intact in the 6pm showing of the flashback clip episode "Shades of Grey".
California Doubling: Lore's Rogue Borg compound in "Descent" is The House of the Book performance hall and library building at the American Jewish University, Brandeis-Bardin Campus in Simi Valley, California.
Many episodes feature Riker playing the trombone, because Jonathan Frakes really does play trombone. And the episode "Data's Day" features Dr. Crusher teaching Data how to dance, because Gates McFadden is an accomplished dancer and choreographer.
Patrick Stewart reciting Shakespeare. Well, they had to get it in there somehow.
Both Patrick Stewart and Brent Spiner get a chance to show off their pipes. Picard leads his men in a sea shanty on not one, but two occasions: as an alien facsimile in "Allegiance", and in Insurrection (where he and Data sing "A British Tar" with relish).
Wil Wheaton would like you to know he hated Wesley as much as you, thank you.
The cast hated "Angel One" and demanded changes. Believe it or not, the first draft was even more sexist. There's no salvaging "Code of Honor", though.
Don't even get Marina Sirtis started on her costuming. Her outfit in the first episode was described by her as "a Wendy's waitress with a very short skirt." But that's nothing compared to "The Ugly Grey Spacesuit" for the rest of the first season. And she hated the green dress, for one simple reason - she had to wear a corset under it.
"Patrick Stewart WILL NEVER BE MENTIONED AGAIN in connection with Star Trek!" — actual memo from Gene Roddenberry. Fortunately, Patrick had a champion in Rick Berman, director Corey Allan, and others who helped rig the auditions in his favor. From the Blu-Ray TNG reunion:
Michael Dorn: Two seasons later, he's like, "...what is he still doing here?!" Jonathan Frakes: "I told them NO!"
With the high profile of The Next Generation securing his position, Roddenberry was able to leverage more control over the tie-ins set inside his universe. His archivist, Richard Arnold, immediately began cleaning house. The on-going DC ComicsStar Trek series was immediately cancelled and retconned, replaced with a follow-up that would be much more in tune with the TV series. (Plus one that didnt deal in as many original or non-canon characters.) Arnold also went to work on the novels, bringing his strict editorial sensibilities to bear. Arnold has had a number of choice comments about how he views the writers of tie-in materials, going to far as to suggest that many of the tie-in writers had never written Star Trek.
Rick Berman was installed on the show by the studio as a way to keep a handle on the show: keep it under-budget, make sure that the scripts were done on time, filter out any adult material. Ultimately, Berman ended up in control because he played the politics game more effectively, season 2 showrunner Maurice Hurley lost his patience dealing with Gene Roddenberry and quit, and Gene was completely toothless at this time, having driven away all of his allies and handed creative control over to his lawyer, Leonard Maizlish. Maizlish is the big bogeyman of the Trek world. However, he is credited with keeping the name "Data", casting John de Lancie and hiring Hurley, which resulted in the debut of the Borg.
One of Ron Moores complaints about TNG was that the characters were not allowed to breathe as individuals or embrace other cultures besides Starfleet. You can almost smell his disdain in episodes he penned himself.
According to his book, Resistance is Futile: Assimilating Star Trek, Ira Behr had similar frustrations. Even after Gene passed away, his in-house directorial style lingered and made it difficult to affect lasting change on any of these characters. Both Ira and Moore would jump ship to DS9. That show was scripted in large part as an adolescent reaction to TNG and Gene's somewhat cranky views.
Descended Creator: Roddenberry's wife Majel Barrett, who also played Lwaxana Troi, owned a great deal of the rights and was one of the chief executives owning Star Trek after her husband's death.
Development Gag: "The Schizoid Man" was originally to have guest-starred Patrick McGoohan; the title of the episode is the same as that of an episode from his famous series The Prisoner (1967). Even though McGoohan did not appear in the episode, the title remained unchanged as a tribute.
Directed by Cast Member: Stewart, Frakes, Burton and McFadden all directed episodes. McFadden also choreographed the dance sequences in "Data's Day", Frakes directed two of the movies, and Dorn directed several episodes of DS9.
Disabled Character, Disabled Actor: Stage actor Howie Seago, who is deaf in real life, played the deaf negotiator, Riva, in season 2's "Loud As A Whisper." The episode was actually Seago's idea; he'd approached the producers about disability representation, and cast and crew worked closely with him to create the episode. Notably, they rewrote the original ending, where Riva somehow learns to speak, after Seago objected.
Howie Seago: I told them I couldn't do that because it would perpetuate the psychological harm that's done now in forcing deaf children to use their voice whether they can or not. I didn't want hearing parents to use the show to perpetuate the oppression of their children. And they [the producers] understood that. I was expecting them to be more intractable. That was a real, honest-to-God relief for me and a credit to the producers, not only in accepting the idea but in executing and designing it properly.
Doing It for the Art: TNG's Blu-ray release was a love letter to the fans and Mike Okuda was brought in to make sure that the remastering was of the highest quality. Because TV production practices of the 80's and 90's involved shooting on film but then scanning the footage onto videotape for editing, there were no completed reels that could be used. Instead, the original raw footage was restored and scanned in its entirety and editors then did a frame-by-frame recreation of each episode. Brand-new special effects were also commissioned as needed to to better fit in with the brighter and clearer images. The end result was universally praised for its quality, especially in comparison to the divisive nature of the Original Series' use of CGI to replace effects wholesale. Unfortunately, the TNG Blu-ray didn't sell well enough to warrant DS9 and Voyager receiving similar treatment.
Is what got Patrick Stewart an audition in the first place! The casting director saw him in a play and wanted him to try out, but Roddenberry was against it - feeling Stewart was too old and too bald to play Picard. Rick Berman admitted to also having doubts, but he was at least willing to give Stewart a shot. Berman, the casting director and production manager Robert H. Justman kept pressuring Roddenberry until he finally relented to seeing Stewart audition.
A minor example having to do with the score. "The Drumhead" is the last episode to be scored by Ron Jones before the brilliant Rick Berman (not the soundest policy maker in the Trek franchise) fired him to try out new composers. Theres a reason why people vividly remember the score to "The Best of Both Worlds" but why nobody remembers anything from the last three seasons of TNG. It wasn't until the latter half of Star Trek: Enterprise — barring the odd one-off composer managing to produce a decent score, and then usually being banned from working on the show again — that the composers were finally allowed to produce anything other than Berman's favored "sonic wallpaper."
Believe it or not, Riker's beard was the subject of intense meddling, with Rick Berman and Gene Roddenberry literally drawing on Jonathan Frakes' face as they tried to figure out how they wanted it to be styled. This went on for weeks, with bits being shaved off and hair being glued back on, until everyone decided (six episodes into Season 2) that they found a style that worked. Then Paramount issued a memo saying that they wanted the beard to be "reduced by 2%".
This hit a lot of episodes in the first two seasons, as there was a rule that a writer was only allowed to produce two drafts of any given script before the showrunner (Roddenberry early on, then Maurice Hurley until the end of Season 2) took over all further rewrites. Michael Piller quickly ditched that rule after he came on-board as showrunner a few episodes into Season 3.
Executive Veto: Apparently Tracey Tormé has originally wanted to include an Andorian in "Conspiracy", but was informed by a producer (probably Berman) that, We dont do antennae on this show. As such, the Bolians were rolled in as a compromise: blue, antennae-less aliens. Later, DS9 writer and producer Robert Hewitt Wolfe reported that producer Rick Berman did not care for the antennae, and noted that, if wed been allowed to, I guarantee wedve put an Andorian on the show so fast your head wouldve spun. The Andorians were finally given their day on Enterprise, appearing in several episodes throughout the series.
Exiled from Continuity: Gene Roddenberry originally ruled that none of the TOS races and worlds (Vulcans, Klingons, Romulans...) would appear in TNG. The original characters as well as their possible offspring were also forbidden. This rule was obviously relaxed from the start, with the presence of Worf and Bones McCoy in the pilot, and totally rejected by the third season which featured stories centering on all three races.
Fake Brit: Daniel Davis, who played a hologram of Professor James Moriarty and Niles, the snide British butler on The Nanny, hails from the Royal House of Arkansas.
Picard's habit of straightening his uniform is called "the Picard Maneuver" by fans (not to be confused with "the Picard Maneuver" from "The Battle").
Riker's... Unconventional method of sitting down (where he appears to mount the chair like a horse, caused by an old back injury and Johnathan Frakes' excessive height) is similarly known as the "Riker Maneuver."
The Galaxy-class starship is often abbreviated to "GCS".
Hide Your Pregnancy: Gates McFadden was pregnant throughout season 4, including during "Remember Me" which contained a couple of physically demanding stunts that she performed herself (she wasn't aware she was pregnant at that point). Later in the season she is shown almost exclusively wearing her "lab coat" and/or being filmed from the sternum up. Fortunately, Crusher often did wear her lab coat outside of the medical bay, so her sudden constant use of it wasn't quite as noticeable as this trope usually is.
Hostility on the Set: The series had a notorious Troubled Production in its first few seasons, it wasn't until the third season that the production team stabilized and the cast really started to get along.
Denise Crosby was told up front that her character was not going to get much screentime (as they were attempting a replicate the Kirk, Spock and Bones Power Trio with Picard, Crusher and Data) and because her bridge station was directly behind the captain, she would spend all day on set with few lines and often just her legs in the frame. This encouraged her to request to be written out.
Gates McFadden was vocal about the sexism and racism that turned up in the first season (especially "Code of Honor"), which she attributed to her time in a theater conservatory that encouraged such feedback. This did not help the already difficult writers room (they notoriously went through dozens of writers, many of whom were hired and fired in the same week), and once Maurice Hurley took control for the second season he demanded that she be fired. Once Hurley left and Michael Piller took over in the third season he convinced the execs and McFadden herself to return.
Patrick Stewart was uncertain of how successful the show would be, and did not settle into his apartment for years. He was also finicky about being a noted Shakespearean actor in a sci-fi show, and would berate the rest of the cast for joking around in between takes. Famously, when the cast said they were just having fun his response was a very terse "And where in our contract does it say we are here to have 'fun'?" (another incident was more understandable, during a documentary/interview before the show aired the production allowed one of the interviewers to wear his costume, which he did not appreciate). He eventually lightened up and joined in the joking and pranking, although the cast still gives him grief over the "fun" line.
Keep Circulating the Tapes: A VERY rare positive example: The Next Level was a Blu-Ray disc containing four episodes from the series to showcase the restoration work to make it HD. One of the episodes, "Sins of the Father", had a 13 second portion (of Dr. Crusher telling Riker about Worf's nanny) that was upconverted from the standard definition tape because the restoration team couldn't find the original film for that section. After that disc was released, they found the film and had a true HD version of the portion in the episode in time for the Season 3 Blu-Ray release and is the version released on Netflix and CBS. In terms of the version with the 13 seconds upconverted from the SD tape, it will likely be gone if and when the Next Level disc goes out of print. As for this being a rare positive example... well, if you had a choice, would you take the version where 13 seconds are a (relatively well done) upconversion or the one that's completely HD? To make it better, the Season 1 set has a documentary about the restoration that talks about the story behind those 13 seconds, meaning the clip can still be seen for historical reference.
Killed by Request: Denise Crosby wasn't interested in continuing with the series, and requested to be killed off during the first season. She later regretted this choice, and came back as a guest star several times.
In the William Shatner documentary The Captains, Patrick Stewart's behind-the-scenes experiences at TNG share an odd similarity with his character. Stewart, who was stressed out over succeeding the stars of TOS and his long hours, got the cast together and told them to quit goofing off between takes ("We're not here to HAVE FUN!!"); his castmates never let him live that down. In the long run, TNG taught him to do good work and have fun doing it. This is mirrored by Picard's final line of the show when he joins the Bridge Officers' poker game.
The Merch: Next Gen had two distinct toylines. The first, by Galoob, came out during the first few seasons. It featured 3.75" figures (in scale with Star Wars) and smallish, die-cast vehicles including an Enterprise whose saucer detached. A few years later, Playmates Toys came out with its own line, which... let's just say that Next Gen was a landmark moment in toys, even more so than Star Wars. To break it down:
The figures boasted superior sculpting and articulation (though sitting down looked slightly unnatural), there were aliens and villains right in the first run, and the line made incredibly creative use of electronics, with sound effects taken directly from the show! What's more, the show itself provided more than ample inspiration for variants, including the "Holodeck Adventures" line.
Playmates also produced ship toys... gigantic ship toys, often a foot and a half in length or more, with a lot of details accurate to the studio model of the Enterprise especially. These also made use of electronics to reproduce sounds from the show and were a staple of Christmas wishlists for years. A great many sci-fi franchises which followed felt compelled to try and match these toys for quality, often with shaky results.
Playmates held onto the license with its teeth, providing lines for Deep Space Nine, Voyager, the Original Series (which got its own badass boxed-set), the movies, Enterprise, and the first J.J. Abrams movie.
Official Fan-Submitted Content: The series accepted fan-written spec scripts throughout its run. At least four made it into production, and a few more episodes were based on premises supplied by fans.
For his recurring stint on the show, Alexander was re-cast from Jon Steuer to the slightly older Brian Bonsall. Whether Justified or simply a case of the production team being painted into a corner by having Klingon children grow so fast in the first place is anyone's guess.
Spot. Yep. Data's first feline friend was a long-haired Somali, while later ones are played by a generic short-haired tabby. This has caused some Trek authorities to joke that Spot is a shapeshifter in disguise, or else lost his fur in a transporter accident.
It's old news now, but Dwight Schulz's transition from the half-deranged (and so half-sane!) "Howlin' Mad" Murdoch to the buttoned-down, mousey Reginald "Reg" Barclay was a novelty indeed. It paid off: Barclay is equally as — if not more — famous as his Star-Making Role on The A-Team.
Brent Spiner was primarily a comedic actor before being cast as Data. Of all the TNG regulars, Spiner probably goofed off the most between takes, which is why Data is always wearing a semi-menacing grin in behind-the-scenes footage. However, he got to cut loose in " The Outrageous Okona", which had Data practicing his Henny Youngman routine in a comedy club.
TNG had a habit of casting notable TV "bad guys" in benign or heroic roles. Jonathan Frakes is the biggest example, as his career up to that point had been almost entirely villain roles. Others include Harry Groener as Tam Elbrun, John Vickery as Andrus Hagan (he'll be back as a backstabbing Gul in DS9's "Final Chapter"), Ronny Cox as Captain Jellico, Christopher McDonald as Richard Castillo, Paul Sorvino as Worf's brother Nikolai, Robert Knepper as Wyatt Miller (he would later play the heavy in VOY's "Dragon's Teeth"), and Spencer Garrett as Simon Tarses (he would go on to play one of the killer holograms in VOY's "Flesh and Blood"). No such luck for Marc Alaimo, though; he played four bad guys!
Both Wil Wheaton and LeVar Burton were Trekkies at the time of their hiring. Wesley's awestruck reaction to stepping onto the bridge in the pilot is entirely Wheaton himself.
Whoopi Goldberg was a huge fan of the original series and has specifically named Nichelle Nichols as her inspiration for acting. Just before the second season entered production, she called Roddenberry, saying "I am a Star Trek fan, I was a Star Trek fan long before I was ever Whoopi Goldberg and I'm wondering if there's some part I can play in your show?" Roddenberry was so impressed that he re-wrote the bartender character he had intended to introduce for Goldberg.
Reality Subtext: LeVar Burton would often get headaches from the devices on his temples that were used to hold the VISOR in place. Likewise, Geordi would occasionally mention headaches as a side effect of wearing the VISOR.
Probably an aversion with Worf; the DC Star Trek comics had long featured a Klingon in Starfleet named Konom, but his backstory and character are very different from Worf's and Roddenberry probably had a similar idea independently.
Data is derived from the character Xon from the cancelled Star Trek: Phase 2. Xon was a full-blooded Vulcan, the idea being that he would provide a contrast to the vanished Spock—whereas Spock was always denying his human side and embracing his Vulcan, Xon would already be secure in his Vulcan-ness and thus be more intrigued and curious about understanding human emotions. This eventually mutated into the idea of an emotionless android seeking to achieve those human emotions.
Patrick Stewart, on the lookout for the next Ex-Ms. Patrick Stewart, dated Jennifer Hetrick (Vash) during Seasons 3 & 4. They were briefly engaged during "Qpid", but nothing came of it. In 2000, six years after TNG ended, Stewart and producer Wendy Neuss did marry. They divorced three years later.
Early in the show's run and prior to her marriage, Marina Sirtis liked to have flings with male guest stars leading to the cast affectionately and endlessly teasing her about her proclivities even decades later.
Separated-at-Birth Casting: Most of the actors playing blood relatives to cast members look impressively like them. For longevity, Majel Barret very much seemed like Marina Sirtis mother, in "Man of the People" where Sirtis had aging make-up on the similarity became uncanny. There was also Jeremy Kemp as Picard's brother Robert. Then there was the child actors playing Picard, Keiko, Ro and Guinan in "Rascals," David Tristen Burken previously played Picard's nephew in "Family" while Isis Jones also played a younger version of Whoopi Goldberg in Sister Act.
"Skin of Evil" was Denise Crosby's last aired episodenote other than her coming Back for the Dead in an Alternate Timeline in "Yesterday's Enterprise", with her character being killed off. In the previous episode, "Symbiosis" (which was actually filmed later), she's in the background at the end, as Picard and Crusher enter the turbolift. Just as the doors close she waves goodbye to the camera.
In "Qpid", Vash has been transformed into Lady Marian by Q. As they were filming the scene where she paces back and forth in her cell, Jennifer Hetrick tripped over her dress. The director left it in reasoning that a 24th century woman would not be used to walking in 12th-century finery.
The series had a rough ride for its first couple of seasons, mostly due to Gene Roddenberry's declining health, substance abuse, spaced-out mental state, and the ridiculously high turnover rate in his writing staff for the first two seasons. Roddenberry's lawyer took control of the writing staff for most of the first season (supposedly rewriting scripts, against Writers' Guild rules, at one point), leading to the departure of TOS mainstays David Gerrold and D.C. Fontana after he began retaliating against them for complaints (Gerrold left amicably, or so he thought, only to be blackballed after Gene "The Great Bird" Roddenberry told everyone he was fired for his incompetence). Near the end of the season cast member Denise Crosby, who got pissed off at being a glorified extra, also left.
The prototype uniforms smelled bad (spandex retains bodily oils more than the newer cloth uniforms) and gave the actors back problems.
Things got a bit better for the second season where Maurice Hurley took over the writing staff, but since a lot of TV writers chose to sit out the whole 1988-89 season after the 1988 WGA strike it left no more than about four or five writers (two of whom worked as a team) working on the show at any one point. It didn't help that, according to Tracy Torme at least, Hurley didn't get along with anybody and only differed from Roddenberry's lawyer in that he actually had writing experience. There were also rumors that Hurley had a big crush on Gates McFadden and expressed it like any four-year-old would: he had her written out of the second season (replacing her with Dr. Pulaski) when she brushed him off. It wasn't until the third season, when Roddenberry's health wouldn't allow him to even work, which allowed Rick Berman and Michael Piller to gently steal control of the production and the show started to balance out, although even then there were a few bumps along the way, including Piller managing to provoke the entire writing staff he inherited from Hurley into quitting after circulating an insensitively-worded "tips on writing for TV" memo, and Roddenberry still occasionally vetoing story ideas and throwing in bizarre suggestions.
Even by the standards of the first two seasons, the infamous episode "Code of Honor" stands out. One of the two original writers took his name off it after it was heavily rewritten, and that was before the director they hired chose to populate the aliens of the week entirely with African-American guest actors, whom he proceeded to treat like garbage (though apparently he didn't treat the main cast a whole lot better). Eventually Roddenberry decided enough was enough and canned the director, leaving the first assistant director to pick up the pieces for the remainder of the shoot... which just happened to include the episode's big action sequence. Most of the main cast members (Jonathan Frakes, Brent Spiner and Wil Wheaton especially) have had some rather choice words about the episode in recent years. Not to mention that many of the writers felt Roddenberry's rewrite put it beyond any chance of salvation. He had supposedly told one of the two original writers, on another episode, that the Enterprise doesn't fire warning shots ... only to add a scene in this episode where it did exactly that. Gah.
Gates McFadden was essentially fired from the show between the first and second seasons, after some rather stern disagreements with one of the producers (which is understandable considering how infamously troubled that season was.) The mountain of fan letters pouring in (and the ouster of that producer) lead to her coming back.
The seventh and final season of the show would see production troubles return, albeit not to anywhere near the extent as in the first season. The main issue was that the writers were simply running out of ideas, forcing them to rely increasingly on implausible and technobabble-laden plots. This was compounded by new showrunner Jeri Taylor putting a stop to the show's open-submission policy, as she felt the writers were wasting time trying to knock amateur scripts into acceptable shape and that it'd be better to have all the scripts written by experienced professionals from the very start, but this ended up cutting off the flow of new ideas at the worst possible time. On top of that, Taylor also demanded an increased focus on stories prominently featuring Troi and Dr. Crusher, who she felt had been under-utilized in previous seasons, but the writers struggled to actually do this seeing how the most obvious plot routes (the Unresolved Sexual Tension between Troi and Riker, and Crusher and Picard) had been banned by executive producer Rick Berman, eventually causing the writers to resort to the Crack Pairing of Troi and Worf, something that came virtually out of nowhere and was never referenced again after the show ended. The eventual announcement that it would be the show's final season actually helped things out, as they were able to bring back several recurring characters (including Wesley Crusher and Ro Laren) and give closure to their story arcs, before the show ended with a hugely acclaimed finale, "All Good Things".
The series tried hard to avoid this (the music avoided any style that had been popular since the end of the Jazz Age, for example), but the hairstyles, the spandex costumes ("spacesuits" as the cast called them), the set design (especially the oft-criticized "hotel lobby" look of The Bridge and the infamously bland beige and rust carpeting and wall paneling), the "Dustbuster" phasers and the presence of a psychotherapist as a command-level officer firmly fix the early seasons of the series in the 80s. Later seasons went to a wool gabardine two-piece spacesuit, a more angular and weapon-like phaser and modified Counselor Troi's duties in an effort to try to bring the show out of the 80s, but some of the more aggressively period-fixing design choices were stuck through the entire show.
Possible, despite real-world politics, given Trek's timeline with the Eugenics Wars and World War 3.
In "The Royale", Picard refers to Fermat's Last Theorem as having been unsolved for over 800 years. Whoops. This was later corrected in the DS9 episode "Facets".
Also in "The Royale", debris from a NASA spacecraft, which according to this episode took part in a mission in the mid 21st century, are beamed aboard the Enterprise. However, the NASA "Worm logo"◊ seen on the debris was actually replaced by the "Meatball logo"◊ in 1992.
Wag the Director: Patrick Stewart wasn't too thrilled with his stodgy, preachy, apparently sexless Captain in Seasons 1-2, and intimated that he might leave the show if something wasn't done about it. (Actually, the phrase he used according to Ron D. Moore was "there isn't nearly enough shooting and screwing on this show.") The vacation episode, "Captain's Holiday," was tailored-made to please Patrick.
Word of Saint Paul: The Star Trek The Next Generation Technical Manual, in its entry on the Captain's Yacht, includes an out-of-universe sidebar that says "Patrick Stewart informs us the yacht is named Calypso after Jacques Cousteau's vessel", in a way that suggests that, as far as the writers of the Manual are concerned, he should know. This was never confirmed on screen, since the Enterprise-D yacht was never used (or even confirmed to exist), but was nodded to in Star Trek: Insurrection, where the yacht on the Enterprise-E is called the Cousteau.
Also from the technical manual, Rick Sternback had a pet idea for "Cetacean Ops" — literally, navigation research that's being handled by a dozen dolphins being overseen by a couple of whales — in huge underwater tanks throughout the ship. It got a mention in "Yesterday's Enterprise" and "The Perfect Mate", but goes otherwise unregarded by other writers.
Working Title: Star Trek A New Beginning, Star Trek A New Generation, Star Trek The New Generation and Star Trek Enterprise 7 (the latter title is explained by the fact the ship was to be known as the Enterprise 7 rather than the Enterprise D).
Most jarring of all is James Cromwell as the leader of a potential new Federation alliance world in "The Hunted", when he later played Cochrane in Star Trek: First Contact.
He also played Zaglom Shrek in "Birthright", and Hanok in "Starship Down" (DS9), though you can't see his face in those.
Marc Alaimo appeared as a minor Rubber-Forehead Alien in Season 1's "Lonely Among Us"; Romulan Commander Tebok later that season in "The Neutral Zone"; a 19th century gambler in Season 5's "Time's Arrow"; and most notably, he played the first-ever Cardassian in Star Trek, Gul Macet in "The Wounded". Marc Alaimo would become, in Deep Space Nine, Gul Dukat, the main adversary of Captain Sisko.
Max Grodenchik as the very typical conniving, treacherous Ferengi Sovak in "Captain's Holiday"; better known for his later role as the very atypical (and somewhat dim) Rom from DS9.
Armin Shimerman played both Letek, one of the first Ferengi ever shown onscreen in " The Last Outpost", another Ferengi, Bractor in " Peak Performance", and the better known Quark — from Deep Space Nine. He also briefly appeared in "Haven" as the Betazoid Gift Box, though it's a bit hard to recognize that one.
Look out for the future Tuvok (Tim Russ) playing a human terrorist in "Starship Mine" (and, ironically, being the recipient of a Vulcan nerve pinch.) He also plays an unnamed human bridge crew member in the 23rd century in Generations.
Robert Duncan McNeill, Voyager's Tom Paris, as Nicholas Locarno in " The First Duty". (The character of Locarno was the inspiration for Paris.)
The Voyager creators say they didn't plan to hire the same actor; once they realized they had, they considered making McNeill Locarno on Voyager, but reformulated him into Paris, feeling that Locarno "couldn't be redeemed enough" (read: they didn't want to pay royalties) for what they planned with Paris.
Hey, that Ferengi doctor in "Ménage à Troi" sure sounds a lot like Neelix... At one point on Voyager ("False Profits"), Neelix is forced to get makeup and surgery so that he looks like the Grand Nagus of the Ferengi, and the actor pulls it off again with great aplomb. Said actor would go on to be one of the 'first' Ferengi ever, in the ENT episode "Acquisition".
Also, keep an eye out for Phillips in Star Trek: First Contact. He is the holographic maître d' who tries to boot the Borg out of his club, saying they aren't dressed properly.
Patricia Tallman, known for playing Lyta the telepath on B5, has a Memory Alpha entry as long as Patrick Stewart himself. Before she got her break, she was a stunt double◊ for the female leads on TNG (barring Whoopi), along with a few on DS9. She also has uncredited roles as a petty officer ("Power Play"), a Klingon (Generations), and a space siren in Star Trek: Voyager ("Fortunate Son").
She only had two speaking roles in Star Trek: one of the hijackers "Starship Mine", and the fake Romulan in "Timescape."
W. Morgan Sheppard is a name which may be familiar to you: Star Trek, Babylon 5, and even Doctor Who. He's first seen here in "The Schizoid Man" as Data's 'uncle'. You can also watch him as a Klingon in Star Trek VI and the Ahab-like alien in VOY's "Bliss".
Most recently, he was told to get stuffed (figuratively speaking) by Zachary Quinto in the Abrams Star Trek movie.
Roy Brocksmth had one-shot appearances here and in DS9: As a Zakdorn in "Peak Performance" and a Bajoran smuggler in "Indiscretion". His most famous role, however, is Dr. Edgemar in Total Recall (1990).
James Sloyan is an authoritative actor who has played four aliens, usually with some sort of dark secret attached. He also died often: Admiral Jerok in "The Defector" (suicide), Future!Alexander in "Firstborn" (erased from history), and Jetrel in the eponymous VOY episode (terminal disease). He also had a recurring role on DS9 as Odo's "father", Dr. Mora.
Eric Pierpoint had guest roles in all four spinoffs: a shape-shifter who attempted to try it on with Picard (" Liaisons"), a Starfleet Captain in "For the Uniform" (DS9), the Klingons' answer to Judas Iscariot in "Barge of the Dead" (VOY), a big game hunter in "Rogue Planet" (ENT), and a Section 31 honcho during the Terra Prime arc (ENT). He is probably best known for his role as Det. Francisco in the cult show Alien Nation.
John Vickery had a good hit rate: Going from a (mute) Betazed in "Night Terrors", to a Cardassian Gul in four episodes of DS9, to Klingon prosecutor in an ENT episode, "Judgement". Babylon 5 aficionados know him as Neroon.
Suzie Plakson as Selar, K'ehlyr, and the female Q on Voyager, to name one.
Urban Legend of Zelda: The operator's manual for the Star Trek: The Next Generation pinball mentions a "secret Video Mode" in the gamenote allegedly a version of Breakout, and there are two operator settings to control it. Problem is, no one knows how to activate it, and it's unclear if the mode is actually enabled in the final game or not. It can sometimes be seen on the display in the game's attract mode, however.