I may no longer be a homeschool mom, but I still encourage creative writing as much as possible:
You can buy these online (Think Geek has a version of them, and everyone should shop there for no other reason than THEY'RE AMAZING) or you can make them yourself like I did with a magnet sheet from Avery.
As soon as I made the first sheet and put my own messages on the fridge (these are Rachel's) everyone demanded I make lots more, right away. So, I'll be making more. :o) Make some yourself, or go buy some and have a little fridge fun in your house. Fun message possibilities are endless!