Oil Drip Pan Chalkboards! Spray prime the drip pans with gray primer, and then use latex chalkboard paint. Tape a border around the edge of the drip pan so it will create a 'frame' of sorts. Hang the boards/pans using 3M Command Strips (4 medium sized ones did the trick).
This is an inexpensive way to add another fun dimension to a kids bedroom or playroom - an $11 oil drip pan from Walmart and a bunch of kid friendly magnets and you have yourself a big ol' toddler sized wall o' fun.