I was just reminded of how much I love J.G. Ballard. He's not so much pure sci-fi these days, but I do think he's one of the best writers around, full stop. His recent stuff (Millennium People, Cocaine Nights, Super Cannes) is really, really good: lurid, apocalyptic detective stories.
His earlier stuff (The Crystal World, The Drowned World, Concrete Jungle and a bunch more I haven't read), which was definitely sci-fi, is pretty prescient - it's mostly environmental/survivalist horror kind of stuff. His whole oeuvre makes for uncomfortable reading these days, because he's probably right about everything, and that's bad news for us.