The Hunger Games by Suzanne Collins is a recent YA sci-fi read. It has a Battle Royale style plot in a futuristic dystopian world.
Haven't yet read the sequel Catching Fire but my sister says its great. One book of the trilogy remains.
Also, I second the recommendations for Ender's Game and the Wrinkle in Time Quintet. If you enjoyed Ender's Game, then Ender's Shadow is another thrilling read. It takes the same major events of EG and explores them from the perspective of another character, Bean.