EDIT: This is no longer available.
This free Science and Technology of WWII poster is only available for teachers, but it's the best freebie I've found so far today. You might be able to request one even if you're not a teacher though and then maybe send it with your kid to school in the fall? Hopefully they have a picture of a Spitfire on here because it's by far one of the coolest plane ever. How can you not love a plane with a name as awesome as that? In fact, I don't care what my future wife says, I've just decided on the name of my first born. Aren't I a catch, ladies?