Farscape
Astronaut John Crichton is flung across the universe via wormhole, and finds himself smack dab in the middle of a vast interstellar conflict between several alien races. Adopted by a misfit crew aboard a sentient spaceship, Crichton finds himself sucked into the war even as he tries to find a way home. Cool aliens (created by Jim Henson), intriguing character development, and sexy humor made this show a fan favorite for the ages.
V
Beautiful alien visitors arrive, promising to help humanity and provide peace and prosperity... but it turns out they're actually evil lizard people, bent on enslaving us. This always-great premise is an excuse for lots of fun paranoia, but also crazy action sequences, like a lone woman standing her ground and shooting at a spaceship with her handgun. This show made alien-fighting fun again.
Fringe
Created by Nerd Pack JJ Abrams, Roberto Orci, and Alex Kurtzman, Fringe follows the increasingly weird and transdimensional adventures of a team that investigates "fringe science" events. As the mad scientist, special investigator, and mercenary researcher get closer to understanding the science conspiracy at the heart of the tale, they discover that their own lives are bound up in it. Scary, silly, and head-explodingly gross, Fringe became an instant classic when it debuted last year.
Stargate SG-1
Stargate SG-1 took the successful film and managed to turn it into an insane ten seasons of adventure, by showing what happened when the military continued to use the space travel Gate technology. Richard Dean Anderson heads up a strong cast, jumping between worlds and defending Earth from alien attacks from the Goa'uld or Borg-esue Replicators. This show established Stargate as the light hearted space soap opera for anyone just looking for a laugh and a bit of suspense. Come for the cheap Gate effects, stay for RDA.
Dollhouse
It's hard to think of a TV show that's created as much controversy in recent years as this one — people see its mind-wiped slaves-for-hire premise as a metaphor for rape, prostitution or just plain slavery. But creator Joss Whedon has been going out of his way to push people's buttons — and now it turns out that the supposedly fun fantasy-fulfillment of being able to hire a programmed human really does destroy the human race in the end.
The Tick (animated)
The Tick broke down superhero conventions and rebuilt them in its own warped image. From the oddball costumed heroes (Wonder Woman and Batman somehow become American Maid and Der Fledermaus) to the villainous plots (Chairface Chippendale gets three letters into writing his name on the moon — a fact that continues throughout the series) to the Tick's superhero banter ("Spoooooooon!"), The Tick is a witty and often surprising parody.
Futurama
Pizza boy Philip J. Fry is cryogenically frozen in 1999 and wakes up a thousand years later to a world of alcoholic robots, predestination paradoxes, and celebrity heads kept alive in jars. It takes repeated watchings to fully appreciate the hilariously jam-packed send-ups of pop culture in general and science fiction in particular, but you'll need a pause button and a firm understanding of mathematics to get all the jokes lurking in the background.
Star Trek: Deep Space Nine
Where most Star Trek series focused on the thrill of exploration, Deep Space Nine treated the Star Trek universe as a real place, fleshing out the politics of the previous series and focusing on the special challenges of a frontier outpost. With the newly liberated planet of Bajor on side of the nearby wormhole and a looming fascist empire on the other, DS9 examined the ethics of terrorism, exposed the seedy underbelly of the Federation, and reminded us that war is hell, even in the 24th Century.
The Twilight Zone
One of the most iconic television shows of the twentieth century, Twilight Zone started in the late 1950s and launched the careers of dozens of actors (including William Shatner) and writers. An anthology series, each weird episode was introduced by Rod Serling, who usually explained its moral too. Tales of aliens, monsters, and the unknown were interwoven with noir-ish stories of people in bizarrely bleak situations. A mix of scifi an existentialism, it defined an entire generation of smart, dark SF.
Blake's 7
Imagine a show that takes place entirely in Star Trek's mirror universe, and you've sort of got Blake's 7. The Federation is evil and oppressive, and only a gang of criminals led by a political dissident stand for freedom. At its absolute best, this show was an unflinching examination of a totalitarian society in denial. (The war-crimes trial episode is absolutely priceless) as well as an exploration into how far our freedom-fighters can go and still remain "the good guys." And it has possibly the best ending in science-fiction history.