Electrocity is one of those games. Plus it's free, and it's online, so kids can play it from any computer with the internet.
I haven't spent much time with it, but some of my students, once getting a taste for it, have gone home and played for hours, trying to get the perfect balance of meeting a city's energy needs without destroying the environment. At the end it gives you a score and grades.
I'm fighting the temptation to go on about philosophies about using games in the classroom.