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".
Hi Less Wrong,
I've got the opportunity to promote books and other forms of content to a largely teenage audience. I'm looking for some good book recommendations and recommendations for a limited amount of other media (websites, movies, etc) that will spread awareness of positive ideas and issues in the world, while still being entertaining to the target audience. HPMOR comes to mind, and although I don't think its main focus is to promote an issue to readers, it is an excellent choice because it is well ranked, promotes rationality which can directly help readers, and is completely free to read online. Recommendations don't have to be free, but that is a very important factor.
Thanks everyone!
Edit: Thanks everyone for your contributions. I realize I was being a little too vague, I think content that promotes ethical/altruistic behavior is mainly what I am looking for, either inspiring it with fiction or causing motivation for it with nonfiction. I am looking for free web content, although paid content recommendations are also appreciated. This is for a general youth audience, not a club or any sort of interest group.