Mention of Superman and BEWITCHED started me thinking about "aliens" of various kinds in TV series. The witches and warlocks in BEWITCHED are clearly intended as a separate subspecies of humanity, so that show counts as "alien romance." A little later, there was I DREAM OF JEANNIE -- of course, not at all like the alien djinn romances by Rowena Cherry (www.rowenacherry.com). Jeannie, from what I remember of the few episodes I watched, was a nonhuman version of a stereotypical pre-women's-lib wife/girlfriend, even more retro than Samantha. All that "yes, master" routine. The first TV series I recall that attempted to create a radically alien extraterrestrial, although humorously, was MORK AND MINDY. That show definitely involved SF romance, since the couple got married and had a son. Mork's species displayed reproductive oddities such as male pregnancy and children being born adult-size and growing down instead of up. All these elements were played for laughs, though.
Vincent on BEAUTY AND THE BEAST qualifies as alien, at least in appearance. We never learned his origin. For all we know, he could have been abandoned on Earth by extraterrestrials. In personality, however, he comes across as more human than human, more generous and noble than the average man. He displays "beast" traits toward the end of the series, when "Dark Vincent" bursts forth. Perhaps his kindness and nobility masked a deeply repressed dark side all along? When he and Catherine produced a child, I was disappointed that the baby, when we finally saw him, turned out completely human in appearance. I wanted to see a furry miniature Vincent!
ALIEN NATION, of all the SF network series set on Earth, tried the most seriously to explore genuinely alien biology and culture. In the category of reproduction, the aliens had three sexes and male pregnancy. These elements were treated in some detail and quite convincingly, such as the episode in which the unborn baby is transferred into George's pouch from his wife's body. Matt, the human detective, had a love affair with an alien woman. Early in their relationship, she confronted him on his speciesest attitudes, his expectations that she ought to be more like an Earth woman. "You think I should have hair," as she said in one memorable line. Later, they took a class on human-alien sexuality together.
The genetically engineered characters in DARK ANGEL might be considered aliens in a sense, not being entirely human. They were bred by combining human and animal DNA. Max, the heroine, had cat DNA. Later in the series we met "cousins" of hers who more visibly displayed the traits of the animals whose genes they carried, such as her part-dog friend. About the time Max and her regular-human guy friend finally admitted their mutual attraction, a villain infected her with a virus specific to him, so that if they touched, he would die.
Did anyone here watch the series STARMAN'S SON, a spinoff from the movie STARMAN? The TV show didn't last long, and I never got around to watching it. Any potential for alien-human romance there? In my opinion, the movie was fun, even though it used a trope that has become something of a cliche, government agents pursuing the alien visitor to lock him up for their devious purposes or simply out of paranoid fear. At the time I saw it, I thought of it as "ET with sex."
What about THIRD ROCK FROM THE SUN? I didn't watch it often enough to know whether it involved much human-alien romance? One interesting facet, as I recall, was that the aliens chose their sexes arbitrarily when they assumed human form for their undercover mission, a detail that implies they didn't have the same gender divisions we do. Did the show ever address the issue of their "natural" sexuality in their true forms?
And of course, branching out to SF programs not set on Earth, the various STAR TREK series often involved romances between human characters and extraterrestrials. We've already discussed Odo the amorphous blob, but there are many other examples, such as human-Klingon and human-Vulcan relationships.
Have I missed any TV series with alien romance elements? I didn't follow BABYLON 5, and I have never got around to watching any of the original programming on the Sci-Fi channel.