This week I went looking for posters that show how the different radio frequncies are allocated. If you are American, you can get a PDF version, or order one from the National Telecommunications and Information Administration (cost: USD $4.25). The Canadian equivalent is available from Industry Canada. If you contact them, they will mail you free printed copies. This should make for a nice decoration in our lab at school. ThinkGeek also sells a more generic electromagnetic radiation poster that would be perfect for a physics classroom.