Just ran into a post :
SF authors as high school students (observing the cafeteria at lunch time) which is more amusing than it has any right being. I've read the vast majority of the authors mentioned, and would recommend most of them.
Speaking of which, I've been meaning to write a long post recommending some F&SF books I've read recently. I don't seem to be getting around to here, so here's the thumbnail version:
The Steerswoman series, by Rosemary Kirstein. Starts out like generic fantasy, but actually SF in disguise. The main character is a "Steerwoman" -- someone who is trained as a natural scientist (in a medieval-tech world) who roams around investigating. The culture is that she will answer any question asked of her truthfully, and in exchange her questions must be answered (or no steerswoman will ever answer yours again). Nice slow world building, and a neat main character whose driving force is her curiosity and intellect. The series isn't finished (and there was a long gap between the first two and the next one), but the books stand on their own fairly well.
New Amsterdam, by Elizabeth Bear. Turn-of-the-20th-century alternate history (US is still a British colony, with lots of complicated politics), in a world with open sorcery, vampires, etc. A series of interconnected mystery novellas featuring a millennium-old vampire and a forensic sorceress with very matter-of-fact, alterna-science style sorcery. Yes, the characters are stereotypes (which the author clearly knows), but the world she creates is a lot of fun. Good lightweight entertainment.
Name of the Wind, by Patrick Rothfuss. First in a (planned) series of doorstop fantasy novels. Nothing spectacular about the background here -- it's a low-tech fantasy world; a brief summary would make it sound unremarkable (there's no heroic quest or long-lost heir; it's not trite, but the setting isn't particularly noteworthy). The worldbuilding, while not innovative, is very solid. There's a well thought through and fairly handled magical system; you get a fair bit of the theoretical background, which is pretty cool. The characters are complex and believable, and it's well crafted and written. This one is, roughly, the main characters coming-of-age tale; there's a lot of potential to build on in the next two books. It merits the many high reviews that you'll find on the Amazon page.