This is, famously, why Asimov wrote his award-winning The Gods Themselves: as if to prove he of course could do it, but usually didn’t want to.
The Medusans, also. Mildly interesting concept, but man, what a pointlessly sexist episode.
Liquid Sky - the aliens are invisible and their spaceship is the size of a dinner plate. I’m not particularly into sci-fi but this movie was amazing.
And the Aquatics.
And from Kirk-era Trek, the Horta. NO KILL I. And of course all the incorporeal superbeings Kirk came across.
Lexx, Moya in Farscape and such living ships.
In Babylon 5, the various First Ones (including Vorlons and Shadows), and the hunch-backed and tentacle-faced Pakhmara.
The Nanites that become self aware in one of Wesley’s experiments in an episode of TNG. Also from TNG the “ugly bags of mostly water” aliens.
But in truth, everybody wants prosthetic foreheads on their real heads.
The sapient black hole from Eater by Gregory Benford.
The Darmats from Starplex by Robert J Sawyer; they aren’t even entirely made of normal matter, but are planet sized entities largely made of dark matter.
The Tines from Vernor Vinge’s Zones of Thought setting. Wolflike creatures that come in packs of 6-8; the pack is sapient, while the individual bodies are only components of the overall mind. The bodies are linked together by ultrasound to form the group-mind, which can long outlast any particular individual body.
The TV trope for this is “Starfish Alien” http://tvtropes.org/pmwiki/pmwiki.php/Main/StarfishAliens
Dosadi Experiment and Whipping Star by Frank Herbert had some pretty neat aliens.
Beat me to it. Weinbaum set the bar very high, very early on. Other than a few dated points, it’s astonishing how casually realistic, believable and yet utterly strange this story is, 75 years on.
There’s an adventure in Traveller 2300 where the PCs encounter hyper-dimensional beings building ramparts against the galaxy’s central black hole. An unlucky PC might get herself rotated through a 4th dimension.
IIRC, he was chided by someone for not writing sex scenes. He decided to do it, but created an alien race that had three sexes, making the sex scene somewhat unusual.
When K. A. Applegate starting writing the Animorphs originally the Andalites were just going to be standard Grays, but her editor encouraged her to make the aliens as alien as possible. Which she did. Then a low-budget TV series was made. :smack:
The Blob.
Also, the Vashta Nerada (the Shadows) from Doctor Who.
Hoovaloo - an extremely intelligent shade of blue.
Well said by both. If an alien is not in some sense humanoid - either in apearance or at least in motivation (even the space creature of Next Gen’s Episode 1, “Encounter at Farpoint”, had a human-like motivation, love) then it is just not going to be all that interesting as a character. Not unless the writers are extremely gifted. And if they are not characters then they are no more interesting than the volcano eruption or star explosion threats that occur which characters must deal with. Important parts of the plot but not what typically actually interests us as readers/viewers.
“We are vreeeendds - Ouch!”
The concept of Galactus - a being who eats planets for food and uses another species to help find the food planets. How Galactus has played out in the various comic books and the movie is very different from the concept.
How about the “mice” in The Hitchthiker’s Guide to the Galaxy, which aren’t really mice at all, but rather just the physical protrusions into our dimension of a race of hyperintelligent pan-dimensional beings?
Another vote for the Horta.
I don’t know if Galactus would be considered an alien. Isn’t he more like an aspect of the universe?
The Xenomorphs from the Alien franchise take on characteristics of whatever species they infect/parasitize–like humans, a predator, and a dog. What would they look like if they infected some non-four appendage species?
ETA: Like the Horta?
Yep–that’s the one. Thanks! They’re the most alien aliens I’ve ever encountered in a book.