This is a good thread from my POV (which I'm resurrecting on behalf of the
Is science fiction still a male-dominated genre? thread) in that a zillion authors I don't have are mentioned and every female SF author I have on my shelves is mentioned except two. I'm not sure how good
Sarah Zettel is and she's since switched completely to fantasy, but she started out in SF.
The one author who really has to be mentioned is
Katherine MacLean. She didn't write a whole lot, but
The Diploids is a fantastic collection and
The Missing Man is a fixup almost as good as the title novella, which is superb and won a Nebula. She's also interesting for being one of the very few female authors (C.L. Moore being another, mostly in the 40s) who regularly sold to Campbell (mostly in the 50s).
In terms of the others mentioned (first poster I noticed mention them in italics) just some IMOs:
Amalthea
Ursula Le Guin - Not my favorite, but inarguably important. Best stuff is
The Left Hand of Darkness,
The Lathe of Heaven,
The Dispossessed,
The Winds Twelve Quarters (collection). Generally sociological/psychological/anthropological SF.
C.J. Cherryh - One of my very favorites, at least for her Union/Alliance stuff, especially
The Faded Sun [Trilogy]. Also some of her idiosyncratic early novels like
Wave Without a Shore. And also for her science fantasy Morgaine series. Not much of a story writer, though - more a novelist and even a seriesist. She writes pretty solid straight SF - not ultra-hard, but not noticeably "soft", either.
manephelien
James Tiptree, Jr. - She got too disturbed and disturbing even for me near the end (most of the 80s) but, through the 70s, she produced some of the finest SF stories ever (all of her first four collections (or equivalent) are indispensable) and her first novel,
Up the Walls of the World is nearly equal to them. She did sometimes write on psychological and even gender issues but, prior to her "outing", Robert Silverberg was convinced she was a he, famously insisting her writing was "ineluctably masculine".
Omphalos
Octavia Butler - famous for her novels which I doubt would interest me (I've only read the
Xenogenesis set, which is fine) and she only wrote a handful of stories but they're invariably excellent (which is actually an understatement).
Bloodchild and Other Stories is the must-have.
Pat Cadigan - A fair novelist (my favorite is probably
Synners) but her core is her fantastic, often mordantly funny stories. Start with
Patterns. Famous, as has been mentioned, for being a unique thing: a female cyberpunk. But she'd be pretty unique regardless and not all of her early work pigeonholes neatly into that. She did seem to get kind of stuck later, IMO, writing media ties and yet more cyberpunky things but maybe she'll get out of it. I'm intrigued by the mention of her off-world stories.
Carol Emshwiller - Not really an SF writer for the most part, or only in the loosest, most literary and fantastical fashion, and she's the kind of writer I might ordinarily not be able to stand except that she's so freakin' great. A literary treasure. And, again, one who excels at stories, though I've heard good things about her novels, too.
Pat Murphy - usually more fantasy-tinged, but capable of excellent SF, too.
Points of Departure is the must-have collection.
The City, Not Long After is an excellent, often surreal novel. She won a Nebula for
The Falling Woman.
K. Riehl
C.L. Moore - one of the two Golden Age greats. Brilliantly colorful, visual storytelling and
Judgment Night is a wild almost van Vogtian masterpiece. Yet again, her stories - Jirel (sorry Teresa), Northwest Smith, other, whether in collaboration with Kuttner or not - are wonderful.
Leigh Brackett - ditto. A Burroughs disciple and Bradbury collaborator and successful screenwriter - everything from westerns to a version of
The Empire Strikes Back.
Razorback
Nicola Griffith - another writer who's defected, this time to sort of thriller/crime novels, I believe (I got the first, but haven't read it yet). But
Ammonite and
Slow River are both good and pretty solidly SF. The latter's probably the best.
-- Actually, I said all but two, but
Tanith Lee hasn't been mentioned, I don't think, and has written some somewhat SF things, though is generally a fantasy/horror author. My take on her is currently in flux, though, so I don't know what to say except that the
Biting the Sun duo was neat.