Might as well start with one who lit the fire:
Mary Wollstonecraft Shelley
Frankenstein; or, The Modern Prometheus (1818)
I've read most of Asimov, certainly all his major works, fiction and non-fiction, but he's always seemed a bit cold to me. Clarke? I'm distressed by him.
Ursula K. Le Guin I love like family.
Bumped into Heinlein once, literally, during his final descent into icky weirdness.
Harlan Ellison was always icky, but brilliant. My wife and I had separately disturbing encounters with him before we met and married. Years later my wife and I were walking in Santa Monica and we saw him coming our way. When he saw us he crossed the street. I thought it was me, My wife thought it was her. Only when my wife commented on it did we discover we had another something in common. Sigh. Ellison's last days were sad.
Philip K. Dick is one of my favorites. Maybe because we are both nuts.
Octavia E. Butler ... of course.
Most of the science fiction I read these days is written by women. It's a great tragedy that science fiction was such a boy's club, in the worst way, for most of the twentieth century.
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