Of course, I would have to suggest Orson Scott Card. It's been too long since I've read his Ender's Game series to give any type of short sumary or to explay why I enjoyed it so much, but I really did.
There are 8 books total, 4 in the main Ender's Game series and 4 in the parallel Ender's Shadow series. The first book in each series take place at the same time and are linked up very well, following the story of two young genius boys who are chosen to go to "Battle School" where they will be trained to become future commanders of an invasion fleet to some aliens' homeworld.
The last three books in each series may seem boring to some, but they are full of very high-end philosophical thinking, which I like in a book. OSC's characters are very well-developed, reminding me of something along the lines of Frodo in Lord of the Rings, and they bring up so many facets of so many topics to think about, most of which you can apply to your own life.
It was from these books that I got my current username. A character in the story uses the name Locke (John Locke, the British Philosopher) as a pseudonym to publish his works online. It's funny because I'm named after someone who's named after someone else!
I also enjoyed his book Empire, which is basically about anothe Civil War in the United States in the near future. I'm generally not too much into politics, but those who are may enjoy a look into the future.
PS: OSC has a movie called Ender's Game in the making! Probably not gonna be nearly as good as the book, but hey, it'll be fun to watch!