In the distant future, most our problems will be solved - except racism. Science fiction is full of crazy bigots, who hate aliens, robots and mutants. We list SF's most monstrous racism allegories, below.
Star Trek rules the world of racial allegories with an iron tricorder. There's the amazing "Let This Be Your Last Battlefield," as pictured above - the Cherons are half black, half white, but they discriminate based on which half is which. They're such awful bigots, flames appear in front of their faces whenever they start running. It must make running a marathon kind of a challenge:
Also, in the book New Boundaries In Political Science Fiction, Wanda Raiford makes a strong argument that when Data is put on trial in the episode "Measure Of A Man," it's presented as a version of the Supreme Court's famous Dred Scott case, only this time the court rejects slavery. Also, Spock's "half-breed interference" is frequently brought up, holograms like Voyager's Doctor are discriminated against based on their photons, and alien prejudice is rife. As Tom Lehrer would say, "the Romulans hate the Vulcans, the Bajorans hate the Cardassians, and everyone hates the Ferengi."
Battlestar Galactica - the new version - also gets into racism with the use of the epithet "toaster" for the Cylons. As New Boundaries notes, Baltar's "Head Six" actually refers to "toaster" as a "racial epithet" and pleads with Baltar to stop Cally from saying it in one scene. Baltar ignores her.
Doctor Who's Daleks are basically space Nazis, as writer Terry Nation made clear on a number of occasions. In their origin story, "Genesis Of The Daleks," we see how the dark-haired Kaleds despise the blond-haired (or wigged) Thals, as their genetic inferiors. It's a "dislike for the unlike," as Ian puts it in the first Dalek story. So of course, the sneaky Russell T. Davies finds several ways to make the Daleks into genetic hybrids with other species, mostly humans, in the new series. Plus there are the Silurians, who refer to the humans as apes or ape-descended primitives.
The X-Men used to be an allegory about racism and the "other" in our midst, but these days it's more likely to be about homophobia.
The Chrysalids by John Wyndham also has a strong eugenics theme - the survivors of some kind of holocaust are living in Labrador, and they're fanatically obsessed with purging all genetic abnormalities out of the human race. Like a girl with six toes, or the cool telepathic kids.
Blade Runner's Replicants are created for slavery on the outer worlds, and then hunted down and slaughtered by Deckard and his ilk. Like the Cylons, the Replicants are referred to as "skin-jobs," which Deckard says is a racial epithet. Since the Replicants can pass as human and anyone could be a Replicant, it becomes another fear of the "other among us," like Battlestar.
Top Ten by Alan Moore, Zander Cannon, Gene Ha et al. This classic comics series uses human-robot relations as a clear parallel for those between white and black people, complete with terms like "clicker," "spambo" (instead of "oreo"), and "wetware" (instead of "cracker"). Also, the Godzilla-esque monster characters have aspersions cast on their intelligence on a regular basis. The series is mostly presented from the perspective of non-robots and non-monsters, and we don't really get to know any robots beyond the stereotypes until we meet Ferro-American cop Joe Pi.
Legion of Superheroes. Over the past decade, this comic set in the thirtieth century has dealt a lot with anti-alien sentiment, which has posed a challenge for the mostly alien kids sworn to defend Earth. In the recent Action Comics storyline, the imaginatively named human supremacist Earth Man took charge of the Legion and banished all aliens off the planet, going so far as to suggest Superman was really always from Earth. This remains an ongoing concern in the Legion of Three Worlds.
Titan AE. After the world blows up, aliens have nothing but disgust for the homeless, destitute survivors of humanity.
Terminator: The Sarah Connor Chronicles. As commenter DocWha points out, this show has been pushing the idea of "metal" as a slur against the machines pretty hard lately, including the variant "metal-lover."
The Time Machine. As commenter alphanumeric1971 points out, the whole Morlocks/Eloi thing gets pretty metaphorically charged. Mostly because those Morlocks are always playing their music and stuff.
Babylon 5 Similar to some other shows, B5 showed a lot of racial animosity going on between different species, although the series also deconstructed this whole notion in "The Geometry of Shadows", where the ethnic battle lines are totally arbitrary and change every five years.
Smallville: Kara Zor-El used the apparent racial slur "Red eye" to refer to Martian Manhunter in the seventh season episode "The Cure." Supergirl, how could you?
Heroes this season has pushed the "persecuted mutants" theme pretty hard, and Danko (aka "The Hunter") is a mouthpiece for all sorts of anti-mutant mutterings. They're taking our jobs!
The Teen Titans addresses anti-Tamaranian bias in the episode "Troq," all about the prejudice which Starfire faces. "Do you know what it feels like to be judged simply because of how you look?" Starfire asks, in one of the episode's more sledge-hammery speeches. Luckily, Cyborg does understand... because he's part robot.
Futurama. Everyone has his/her little prejudices - Bender dreams about killing all the humans, for example - but the only group that really faces institutional racism is the mutant population, which isn't allowed to go on the surface unless with special passes (which even then aren't always honored). Although they themselves hate in turn the sub-mutants who live in the sub-sewers. Oh, and Zapp Brannigan really hates the neutral people (but then…what does it take to make a man turn neutral?). Oh, and the Native Martians are a clear allegory for Native Americans, complete with being tricked into giving up their entire planet for just a bead (which turns out to be the biggest diamond in the universe, making it not such a bad deal after all).
The Animatrix – The whole Matrix origin story "The Second Renaissance" uses a lot of really obvious racism parallels to explain how humans and AI came to hate each other.
Planet Of The Apes. I can't believe we left out the 1970s' greatest racism analogy, until commenter UshaBibaculus pointed it out. Damn it all to hell!
Isaac Asimov. Some of his stuff about robots takes on racism overtones, but the condescension of space-going humans towards those still on Earth is way more blatant. Pebble in the Sky has some of the most blatant anti-Earth sentiment, as even the hero, archaeologist Bel Arvadan, considers himself quite progressive and would allow an Earthling to join one of his digs – as long as nobody else objected too strongly. Asimov's short story "The Martian Way" also shows how Earth sentiment against the colonists on Mars forces them to find fuel around the rings of Saturn. Considering the Earth politician who whips up public outcry against the colonists is actually called Hilder, I think it's fairly clear this goes beyond simple dislike. Meanwhile, in the real world, Asimov deleted aliens from his Foundation books entirely because he didn't want to deal with his editor John Campbell's belief that humans would always be superior to aliens, which grew out of his belief in Anglo-Saxon superiority.
Alien Nation. After a bunch of aliens come to live among us in this TV series, they experience prejudice and mistreatment at the hands of the anti-alien Purists. The humans try to kill all of the Binnaums, the rare third gender which the aliens need to mate. Even the most sympathetic human character, Matt, turns out to have anti-alien biases.
The Green-Sky Trilogy by Zilpha Keatley Snyder. These books spend a lot of time delving into the mutual distrust and antipathy between the "fair-skinned, treedwelling Kindar and the darker-skinned, underground race of Erdlings" who live on the eponymous Green-Sky planet.
Wild Cards, created by George R.R. Martin – In a world where aliens test out bioweapons on humanity, creating fully superpowered "Aces" and horribly mutated "Jokers", both groups face bigotry at the hands of humans - although the Jokers generally have a much harder time of it, being horribly mutated and all.
Darkover by Marion Zimmer Bradley. In this series of books about humans colonizing the world Cottman IV after their ship crashes, the native trailmen and catmen face a lot of nasty prejudice from the humans.
Someone Like Me by Tom Holt. This book explores a post-apocalyptic world where the remnants of humanity spend all their time fighting evil, mindless monsters. The only problem with that is that these monsters aren't evil or mindless at all, but in fact just as intelligent and human (with all the attendant strengths and flaws) as the humans, which the human protagonist discovers at the end of the book.
Warchild by Karin Lowachee. Humans assume their alien opponents are mindless cannibals and hate them accordingly. Then the author explores the alien society, and the truth becomes far more complicated.
The Xenogenesis Trilogy by Octavia Butler. The Oankali find humans fascinating and horrifying, and they want to combine with us to create a new species - unfortunately, humans are also revolted by the Oankali, and have a lot of disgust for the half-breed Akin, the first person to result from the intermixing.
Astro Boy. As TVTropes points out, this anime includes robots comparing their planned robot homeland to Israel, and also compares the human treatment of robots to Apartheid. One Japanese robot flees to the United States after almost being lynched. (TVTropes also points to Bubblegum Crisis, Fullmetal Alchemist, Zettai Karen Children, Warhammer 40K and Mass Effect. I wish I'd found that page before we'd already finished researching this post!)
Mr. Show. This list would be hopelessly incomplete without the comedy sketch, "Racist in the Year 3000." We miss Mr. Show.
Additional reporting by Alasdair Wilkins.