A Wrinkle in Time, by Madeleine L'Engle
This book combines fantasy and science in really incredible ways. In this character-driven, thought provoking story, fourteen-year-old Meg travels across the galaxy with her brother and friend Calvin to save her father from some of the dark powers of the universe. I read this book for the first time when I was about nine, and it completely changed the way that I thought about the world.
The Lightning Thief, by Rick Riordan
This book and those that follow it have become really popular in the past couple years. I suppose that they're aimed primarily at middle schoolers, but they're so well written and interesting that I know people of all ages who enjoy them. In this fast-paced, original novel, Percy discovers that his father was the Greek god of the ocean, Poseidon, and finds himself on a quest to recover an object that could start a civil war if it remains lost.
The Mysterious Benedict Society, by Trenton Lee Stewart
This is a slightly less well known book, but it's one of my favorites. Four children are chosen by a secretive man for a secret mission. Mysterious messages are being sent over hidden television and radio signals-- messages that subconsciously effect the way people behave and think. Reynie, Sticky, Kate and Constance are unlikely teammates, but they work together to stop the man sending the messages. The book is action packed and thought-provoking.
The Fault in Our Stars, by John Green.
This book has recently had its praises sung by many people. For those who are hesitant to jump on the bandwagon merely because of its popularity, let me set the record straight: There are two kinds of book-popular. There's Twilight popular, and then there's Harry Potter popular. This book is Harry Potter popular. The Fault in Our Stars is about Hazel, a teenager with terminal cancer. It is a love story, but it's more than that. This book changed the way I thought about everything. It's philosophical, funny, accurate, and heart-breaking. You will be better off for reading it; just trust me on this one. In the words of a friend of mine: "Every time someone reads The Fault in Our Stars, a new galaxy is born. It's THAT GOOD." Warning: You will cry. A lot. I cried over this book more than I have ever cried over any book or movie. Heck, I cried harder than I sometimes do when I feel sad about something in real life. Suffice to say, so many tears were shed that I would not be surprised if Hawaii is now underwater. But it's worth it.