Joanna Russ is probably the most competent of the 1970's writers. All of her stuff is good, but The Female Man is probably her best.
James Tiptree, Jr. is the pseudonym of Alice Sheldon. Her stuff is amazing. There are two novels and a bunch of short stories, and you wont go wrong with much.
Octavia Butler is probably the best female SF writer the world has ever known (at least IMHO). She is mainly a novelist, but there is a book of excellent short stories.
Joan Slonczewski wrote a book called A Door into Ocean. Its not my favorite, but Slonczewski was a Quaker, and the book has a unique voice because of that.
Wilhelm, mentioned above, wrote one of my favorite books of all time called Where Late the Sweet Birds Sang. You should not miss that one.
Madeleine L'Engle write a Newberry Award winner called A Wrinkle in Time. Its a great story, and suitable all around for kids.
Elizabeth Ann Scarborough worte a book called The Healer's War, which is quite good.
Vonda McIntyre wrote a few books, The Moon and The Sun and Dreamsnake are two of the better ones, but she doesnt often miss the mark.
I also really like Nancy Kress, mentioned above. Her first Sleepless book is excellent, and so is the novella it sprang from.
Sheila Finch is starting to make a name for herself, with her Xenolinguist series. I think that there is a novel and a fix up, or maybe an anthology out there.
Mary Doria Russell has two excellent, excellent books out, called The Sparrow, and a sequel whose name I forget. She is probably the most recognizable woman writing SF today.
Pat Cadigan is called "The Queen of Cyperpunk" and was one of the only notable women ever to write in the subgenre, if the only one.
Carol Emshwiller is a strong author from the New Wave era, and she has finally started putting out novels. So far they are pretty good. I have always loved her short stories, and you could spend a lifetime finding them all.
Pat Murphy is still writing. I like her stuff.
So is Eileen Gunn, but Ill be damned if I can ever remember reading anything by her. I just picked up something called Stable Strategies and Others at U-Books in Seattle, so we shall see what she can do.
Kristyn Kathryn Rausch (sp?) is still publishing. I think she and her husband, Dean, used to own a publisher called Axlotl/Pulphouse, which is the firm in the late 80's and early 90's came up with the business plan that is used by PS, Subterranean and many others today, where a trade, a limited and a leatherbound signed are produced in increasingly small numbers and marketed all at the same time, almost identically for each book. They folded.
Kathryn Cramer and Ann VanderMeer are both editors, and they are active now.
There are a few others that I like, but this should get you going.
Check out my book review site. Many of these authors are reviewed there, and soon enough they all will be. This link has them alphabetized by author:
Omphalos' Book Reviews: Browse Books