Best Science Fiction for the Curriculum What do classroom teachers feel are the best science fiction works to introduce in a literature class, and why?

I love classic
scifi like Asimov and Harry Harrison.  I have used Asimov's Three Laws of Robotics in class,
where students tried to find potential problems with those laws and come up with a fourth law
that could solve them.  Harry Harrison (author of "Make Room, Make Room!", which
became the film Soylent Green) is rarely read nowadays, but his stuff all features jaunty heroes
whose hearts of gold are hidden by their gambling or theiving ways. Most of them are pretty
short, and they're lots of fun.

My all-time favorite author is Marion Zimmer
Bradley, who is mostly known for her bestsellerThe Mists of Avalon but was incredibly prolific
and wrote an astonishing number of books. I particularly like her Darkover series, set in a
world where the top technology is psi power, not machine/computer technology.  It does a great
job of using the alternative world to examine conventions in our own world and history,
particularly those having to do with interpersonal communication, gender...