A thread seems a bit sexist at first glance. But the female authors do seem to get less attention than the men around here, so maybe it is useful as affirmative action (whether or not one believes women really write in any different way).
Looking at authors who have written 3+ books/series that i loved, my top 10 is (with books i most liked, and gave 8/10 or more):
Gene Wolfe (BotNS, BotLS, Peace, Fifth Head of Cerberus, Island of Dr. Death, Endangered Species, Latro in the Mist).
Margaret Atwood (Handmaid's Tale, Oryx and Crake, Blind Assassin, Cat's Eye, Alias Grace)
Patricia McKillip (Riddlemaster Trilogy, Forgotten Beasts of Eld, Ombria in shadow, Harrowing the Dragon)
Sheri S. Tepper (Beauty, Grass, Chronicles of Mavin Manyshapped, True Game trilogy, Raising the Stones)
Ursula LeGuin (The Dispossesed, Left Hand of Darkness, Wind's Twelve Quaters, Earthsea quartet, Lathe of Heaven)
Roger Zelazny (Lord of Light, Chronicles of Amber, Doors of His Face, Lamps of His Mouth)
Robert Silverberg (Book of Skulls, Dying Inside, Sailing to Byzantium, The World Inside)
Kelly Link (Stranger things Happen, Magic for Beginners)
So i would say more than half of my favourite authors are female - although in terms of the number of favourite books the men are ahead, due to having read the most famous book of many, then no more.
Others that i think are pretty great, but i've not read enough of yet, so have only one or 2 books on my favourite list:
Octavia E. Butler (Parable of the Sower / Talents, Bloodchild, Wildseed, Dawn)
Carol Emschwiller (I Live with You, Carmen Dog, All her short stories!)
Maureen McHugh (China Mountain Zhang, Mother and Other Monsters)
James Tiptree Jr. (Her Smoke Rose Up Forever, Warm Worlds and Otherwise)
Angela Carter (The Bloody Chamber, Burning Your Boats, The Magic Toyshop)
Catherynne Valente (The Orphan's Tales: In the Night Garden)
Mary Doria Russell (The Sparrow & The Children of God)
Ellen Kushner (Swordspoint, Thomas the Rhymer)