Before hanging decorations on your ceiling, check with your principal. Some schools have fire alarms on the ceiling and hanging things may interfere with seeing the alarm light.
One year my students made globes. It was a great review of the continents and was good for teaching how to work together. It also looked amazing when it was done.
All you need are balloons, newspaper strips, and paper mache paste (1 part flour 2 parts water). Dip the stips into the paste and place on balloon, overlapping as much as possible. Let dry. Once it's dry, stick it with a needle to pop the balloon. The children then paint the globe.
Hang using a paper clip and clear string.
I also made a huge banner to hang with the globes that read "In the Beginning He Created the Heavens and the Earth".