A fantastic book! I was recommended Ender's Game by my little brother, who usually reads these types of books, and it actually was a great recommendation (goes to teach you that even things you may not like can end up surprising you).
Ender's Game is set in the future (Wikipedia tells me it's the year 2135) and is about a genius boy named Ender Wiggin who has been chosen to go to Battleschool. Battleschool is where chosen children go to train for the upcoming invasion of the Buggers, an alien race that everyone on earth has battled previously.
I could go on about the story, but part of the fun was not knowing a) anything about the book and thus b) not knowing what to expect. If you don't traditionally like sci-fi (and I didn't, before this book) you should still give this a shot; Ender's Game will not disappoint, is very cheap, and is a very quick read. Enjoy!