Positive Book and Other Media Recommendations for a Teen Audience

I'm not entirely sure if Terry Pratchett's Discworld series is quite what you want, but I'm mentioning it anyway because it's awesome.

Not sure what you mean by "positive" here. Ethically, what you probably want are works that make you take the perspectives of people different from you, and involve solving problems in creative and effective ways. Maybe I'll try making a list of those later, but right now I'm just going to focus on fiction that might inspire people's problem-solving skills a little.

Top Recommendations:

Online original fiction: Everything written by Ted Chiang (excepting "Understand," perhaps - that is not a story about ethical behavior :P). "The Man Who Bridged The Mist" by Kij Johnson. Possibly some selected Greg Egan stories, possibly Yudkowsky's The Sword of Good.

Book-form fiction: Tons of options here. Rosemary Kirstein's "The Steerswoman's Road" is quite good. Asimov's novel "The Gods Themselves" is a classic (if PG-13), can also direct them to an Asimov anthology like "I, Robot." More classics like Lloyd Alexander's The Iron Ring (one of those kids books that's still good for adults), lots of Ursula LeGuin (particularly her early stuff). Terry Pratchett (probably best to get people started with a later novel like Thief of Time, Small Gods, Wee Free Men, or Making Money).

Fanfiction: Luminosity, HPMOR, most things alexanderwales has written (all good, maybe not all what you want), and the superman fanfic Veritas are all pretty recommendable to general audiences. Another contender would be author Forthwith's My Little Pony short stories (not that their longer stuff isn't also good, it's just not finished).

So You Want to Be a Wizard by Diane Duane.

This is a book/series where the wizards are all working against entropy, at scales from the small and personal (taking care of possessions, being patient with others) to the enormous (shepherding new sentients, saving a planet). And, as the series go on, the choices aren't easy or costless.

Plus, this is the oath you take to be a wizard:

In Life's name and for Life's sake, I say that I will use the Art for nothing but the service of that Life. I will guard growth and ease pain. I will fight to preserve what grows and lives well in its own way; and I will change no object or creature unless its growth and life, or that of the system of which it is part, are threatened. To these ends, in the practice of my Art, I will put aside fear for courage, and death for life, when it is right to do so -- till Universe's end.

Suggestions based on your edit:

Peter Singer, The Life You Can Save

Ursula LeGuin, The Ones Who Walk Away from Omelas

Katherine Boo, Behind the Beautiful Forevers

Albert Camus, The Stranger and The Myth of Sisyphus (preferably read together, since the latter can really help illuminate the former)

HPMOR is an excellent choice.

What's your audience like? A book club (presumed interest in books, but not significantly higher maturity or interest in rationality than baseline), a group of potential LW readers, some average teenagers?

The Martian (Andy Weir) would be a good choice for a book-club-level group- very entertaining to read and promotes useful values. Definitely not of the "awareness raising" genre, though.

If you think a greater than average amount of them would be interested in rationality, I'd consider spending some time on Ted Chiang's work- only short stories at the moment, but very well received, great to read, and brings up some very good points that I'd bet most of your audience hasn't considered.

Edit: Oh, also think about Speaker for the Dead.

Earthsea by Ursula Laguin (sp?) I am also a fan of promoting classic literature whenever possible. I recommend "On the Road" by Jack Kerouac and The Outsiders.

"Little Brother" by Cory Doctorow?

I think Manfred got most of the big ones already, but here's some of other ones that have strong Altruistic/Rationalist/Learning-inspiring/Transhumanist themes:

Online Original Fiction: Many of the short stories by Seth Dickinson, particularly "Economies of Force" and "Sekhmet Hunts the Dying Gnosis: A Computation". Ra, though it can be hard to follow at times. Various short stories written by the author of Ra, though some of these involve are quite confusing. Worm, though that's horrendously long - maybe a couple of interludes? "The Fable of the Dragon-Tyrant", by Nick Bostrom. Yvain's "The Study of Anglophysics". (Though this may inspire world-destroying behavior.)

Book-Fiction: Sophie's World. Peter Watt's Blindsight.

Fanfiction: "Involiate", by Scrivener. "Veritas", by ShaneT, though I can't find it for some reason. Several of the OptimalVerse Fics, particularly "Friendship is Optimal: Caelum est Conterrens".