Reddit reviews Our Spaceship Earth Satellite Map

The American Math Society (the main professional organization for mathematicians) supplies some posters for free to educators. Many of them are probably more appropriate for high-school or college level courses, but some of them might work for you:

• http://www.ams.org/samplings/posters/posters
  
  The "bending it like Bernoulli" poster might be good for younger students, for instance.
  
  A Dymaxion map is also fun, especially if you can find one accompanied by a diagram explaining how it's made. This one looks good, though it's fairly expensive:
  
  
• http://www.amazon.com/Our-Spaceship-Earth-Satellite-Map/dp/B001IYURD2
  
  I'll add that I'm actually pretty shocked at how few posters I could find by Googling. I thought it'd be easy to get a poster of the knot isomorphism classes up to some number of crossings, or demonstrating the Sieve of Eratosthenes, or illustrating why you'd expect seed packings on a pinecone to come in Fibonacci numbers, but I couldn't find anything of the sort. Maybe I need to design some...