"The Handmaid's Tale", by Margaret Atwood.
"Cordelia's Honor", by Lois McMaster Bujold
Frankly I found "The Left Hand of Darkness" to be intensely tedious, and think LeGuin's "The Tombs of Atuan" or "Tehanu" would be better selections from that author -- if only you were teaching a scifi/fantasy class instead of just scifi.
Well, I think we're evenly matched, there, because I found The Handmaid's Tale to be intensely tedious in turn. I think Tehanu's ending is extremely weak, even though I like most of the book better than I did when I first read it. And I wouldn't want to use the later books of a series without using the first one, even if I were teaching a mixed SF/F class.
Cordelia's Honor never struck me as feminist SF in the same way the other works are.
Oh I didn't say that "The Handmaid's Tale" wasn't tedious too; just that for some reason it seems to be mentioned every time feminism is juxtaposed with science fiction (usually in the same breath as "Left Hand of Darkness").
Anyway, while the first book of Cordelia's Honor is not quite as blatantly feminist (though it has its moments), the second book has more meat in that regard. The book has a strong, proactive female protagonist, who (shock! horror!) actually becomes pregnant and is concerned primarily with matrimonial issues (i.e. the survival and health of her child) without becoming weak (which is a break from female characters who have to mimic male warriors in order to be 'strong'). There is also the clash of a gender-egalitarian person with a patriarchal society, which generates some interesting friction and insights. Also, there is the notion of uterine whatshamacallems, and their role in changing society towards gender equality. Finally, there is some rather interesting commentary on how sometimes rapists can be victims too....that should inspire some controversy and debate!
Also its just a fun book.