This New York Times Best Seller is recommended by the US Marine Corp to its recruits. Ender's Game is a novel about human nature, war, ethics and other topics.
The story is fascinating, but I don't want to talk it about it at all because I think a lot of the joy in this story is in patching all the pieces together by yourself as you read.
After I read Ender's Game, I decided to read the prequel and the sequel. The prequel was great as well, but I thought the sequel was a total waste of time. Or maybe I just didn't understand its point.
This link gives you access to all the stories Orson Card wrote about Ender, but I highly recommend reading Ender's Game first before checking out the others.