When it comes to talking about sci-fi television shows that stand the test of time from the 90s, the problem isn't that there aren't enough. The problem is that it appears that period of time was such a heyday for sci-fi programs that it's hard to limit a list to just five titles. For whatever reason, it appears that almost everyone who had an idea for a TV show in this era that dealt with science fiction was like King Midas turning anything they touched into a pile of gold.
Even better than the number of science fiction shows that aired at some point in the 90s is that there was something there for everyone. Viewers who were very into time travel got a show they could say "oh boy" to and call their very own. If someone was more into a show about space exploration and who wanted a bit more Star Trek in their lives, there was a show available to meet that desire. Maybe the focus was about aliens that were visiting the planet in secret? There were plenty of those offerings that were also plenty good. When it comes to five of the shows that really stood the test of time, there were a plethora of programs.
Quantum Leap
If Back to the Future is the preeminent movie about time travel, then Quantum Leap is the same thing when it comes to television. The series, which aired from 1989 to 1993 was quite popular in part because it had a rather original take on just how time travel worked. The premise of this show was that a time travel machine test pilot named Sam (Scott Bakula) who had a bit of an accident with his machine.
The scientist could only go back in time to periods that took place during his life and when he traveled, he actually jumped into the body of someone who needed him to fix some big mistake or terrible incident that happened to them. It also turned out that he was trapped jumping from one event to another and needed the machine to automatically get him home if he ever wanted to stop "leaping" through time. That last detail is interesting if only because Quantum Leap wasn't the only science-fiction show in the 90s that used that premise.
Sliders
Sliders was a show that was remarkably similar to Quantum Leap in one very big way. Rather than traveling through time, a group of adventurers are instead shot into various alternate universes where they have to just try and survive until they can slide into the next one with the hopes that at some point, they'll slide home to their own universe. What makes this show quite similar to Quantum Leap is that the machine that takes them from one universe to another is broken to the point where they cannot mess with it or try and change it.
They have to wait for the timer to run out, take them to the next world and just hope it's theirs. One of the best television science-fiction shows in any era, it got quite a bit of attention because of its focus on what the MCU now calls the multiverse. Considering this program ran from 1995-2000, one has to wonder if they got the idea of a broken device controlling where they go and when from Quantum Leap.
Stargate SG-1
Stargate SG-1 was a series that ran from 1997 to 2007 and was popular enough that it even spawned a couple of different spinoffs. Based on the Stargate movie, it featured a special military organization that was specifically devoted to using the stargate system to travel to distant planets that could never be reached by traditional human starships in one person's lifetime.
The main goal of traveling through these gates was to head off attacks by a number of different alien races that were all more technologically advanced than humans. Unlike both Quantum Leap and Sliders, the people doing the traveling this time around were actually in control of the devices. Along the way, the show ran long enough that the cast changed its makeup a couple of times but one of the members of the cast who managed to go the whole way was Christopher Judge, who is better known as the voice as Kratos in the latest God of War game these days.
Farscape
Farscape squeaks into this list because it got its start in 1999 and ran until 2003. The show features a United States astronaut who finds himself flying through a wormhole and being shot to the other end of the galaxy where he encounters all kinds of different alien races and has to pick a side in some intergalactic fights that he really shouldn't have been involved in.
The show might not have been as popular as some of the other programs on this list, but it is one that heavy-duty science-fiction television show fans will rattle off as one of their favorite sci-fi shows quite quickly. One fun fact from this show is that the American pilot is played by Ben Browder, who eventually joined the Stargate franchise cast.
X-Files
There are few television science-fiction franchises that are more popular than the X-Files. In fact, it's a safe bet there isn't any other television sci-fi program that comes close in popularity to this show. The program has birthed several wannabes and quite a few spoofs, in television, movies, and video games. The X-Files theme song is so well known that even people who didn't watch the show could probably name the program the theme belonged to.
While both David Duchovny and Gillian Anderson have had very successful careers outside of this science-fiction show, they are still almost universally known first as Agent Fox Mulder and Agent Dana Scully respectively. The series was so popular that not only did it birth two different movies but after its original 1993-2002 run, it was actually brought back for two more seasons in 2016.