I admit that I mostly read crime or pulp fiction - easy throwaway stuff - but when I was younger I devoured sci-fi novels. There were many mostly American pulp writers that fed my diet - Bradbury, Asimov and so on.
Most of these were so-so - very few make you sit up and think, "Wow, that was truly mind-blowing - makes you think!" Kurt Vonnegut's Slaughterhouse Five did it for me (but Mother Night was turned into a much-better movie)
There's a current resurgence in sci-fi at the moment with Obama raving about Liu Cixin's Three-Body Problem (I found this hard-going to be honest). Others scream for us to read Wind-Up Girl by Paolo Bacigalupi, Margaret Atwood's The Handmaid's Tale (double hard-going!), Amitav Ghosh's The Calcutta Chromosome or Omar El-Akkad's American War (Texas anyone?)
What did it for you? Which one blew you away and made you think? As far as you know, were there any movie or comic book adaptations?