Long before Harry Potter saved the wizarding world, Ender Wiggin battled the buggers to save the universe. As one of the youngest students ever to enter soldier training, Ender's intelligence and compassion set him apart from his classmates in a number of ways. In each stage of his training, the instructors use isolation techniques to help mold Ender into a commander who they believe holds their only hope of victory against the invading armies of buggers. While Ender is in space making a name for himself, his siblings, left behind on Earth, begin plotting a take-over to gain their own recognition.
You will find Ender's Game on nearly every Top 10 Sci-fi books list, but don't write it off as a simple space story, it is much more than that. Card delivers a story of personal growth and relationships, of society and humanity. His characters are interesting and believable (in relation to the scenario), the plot is engaging with a little surprise thrown in for good measure, and while this is the first in a series, the cliff hanger doesn't leave you unsettled.
This book is being made into a movie expected to come out Fall 2013. I'd recommend reading the book before then, it is fast and fun, and I think has lots of movie potential.