Unlike the fantasy list, these are more favourites than must-reads, partly because there is a lot of SF that I know to be very good but don't personally enjoy reading (Iain M Banks and Octavia Butler are two authors who spring to mind). Also, the line between SF and fantasy is blurry at best, so you might not even agree that some of them are SF in the first place!

1. "The Left Hand of Darkness", by Ursula Le Guin

   A classic of the genre, set on a world of human-like aliens who cyclically change gender. Some of her work is a bit too earnest for my tastes, but her extrapolations from biology and anthropology were such a revelation after a diet of conventional, technology-based SF.

2. The Collected Short Stories of Philip K Dick

   I much prefer Dick's short stories, which are usually witty and insightful, to his novels. I blame them for giving me a taste for reality-bending movies like "Donnie Darko", "The Truman Show" and anything by Charlie Kaufman!

3. "Neuromancer", by William Gibson

   Arguably the book that started the cyberpunk revolution of the eighties. Gibson is also an excellent example of how to handle exposition in SF, gently drawing you into his world without you even noticing the massive amounts of information.

4. "I, Robot", by Isaac Asimov

   One of the first SF books I read, this was the start of a life-long interest in artificial intelligence. His Lije Bailey SF whodunnits were probably what introduced me to crime fiction, so I owe him a double debt!

5. "The Saga of the Exiles" (4 book series), by Julian May

   May intelligently blends science fiction with Celtic mythology in this baroque epic of a group of misfits fleeing six million years into Earth's past.

6. "Hospital Station", by James White

   Another favourite from my early years of SF reading, this collection of short stories set on a multi-species hospital appeals to the biologist in me. Not great literature, but inventive 'hard' SF.

7. "Flowers for Algernon", by Daniel Keyes

   The story of a retarded man named Charly who is chosen for an experiment into intelligence enhancement, movingly told through Charly's own diary.

8. "Alien Taste", by Wen Spencer

   I have to admit a bias here, because Wen is a regular on the Writers BBS forum. However her Ukiah Oregon books are a riveting blend of X-Files-style alien conspiracy, contemporary hard-boiled detective fiction and Native American culture. Somebody buy the TV rights, now!

9. "Man Plus", by Frederick Pohl

   An under-rated classic that thoughtfully examines the man-machine interface. An astronaut is cyber-enhanced to cope with the Martian environment, but the program meant to protect him eventually turns him insane.

10. "The House on the Strand", by Daphne Du Maurier

    A Wellesian tale of a scientist who invents a drug that allows him to see into the past, with addictive and tragic results.