If you like Harry Potter and if you also like science, then you absolutely must read this: Harry Potter and the Methods of Rationality.
It is brilliant. No, really -- incredibly, amazingly, scarily brilliant. It takes some of the history and most of the world of the Harry Potter series (the settings, the politics, the wizarding war) and gives them a twist, resulting in a totally different story. It's Harry Potter as if Ender Wiggins from Ender's Game was the hero.
It is also incredibly funny. I laughed out loud, literally, more than once and a couple times so hard there were tears in my eyes. It's over 500,000 words long so a serious investment of time, but worth every single minute. It's the best thing I've read in...I don't know how long.
A little tiny sample:
"I... see," Professor McGonagall said. "And if, perhaps, you were to discover the entrance to Salazar Slytherin's legendary Chamber of Secrets, an entrance that you and you alone could open..."
"I would close the entrance and report to you at once so that a team of experienced magical archaeologists could be assembled," Harry said promptly. "Then I would open up the entrance again and they would go in very carefully to make sure that there was nothing dangerous. I might go in later to look around, or if they needed me to open up something else, but it would be after the area had been declared clear and they had photographs of how everything looked before people started tromping around their priceless historical site."
Professor McGonagall sat there with her mouth open, staring at him like he'd just turned into a cat.
"It's obvious if you're not a Gryffindor," Harry said kindly."
Yes, it's a Ravenclaw version of Harry. He calculates the odds, he thinks ahead, he uses reason and Bayesian probability and ... really, you should just go read it right now, because it is that good. No, even better than that. Really.