The Worthing Saga

Hard to say... had you asked me this question 15 years ago, I would have answered without hesitation, The Hobbit and Ender's Game. Today, it's a bit less clear, but here is what comes to mind. Rendezvous with Rama - Arthur C. Clarke Worthing Saga - Orson Scott Card

I'm a huge fan of Orson Scott Card, so take the following with a grain of salt. Despite "recent interviews" which most people really disagree with, I still think almost all his fiction works are great. So if you liked Ender's Game, be sure to pick up other fiction books by him. I especially recommend "Songmaster" and "The Worthing Saga".