A 3D model of a comet brings the lesson from the textbook to life for your students.
You can make this with any available art supplies, or you can make edible ones out of candy.
I went to the manager of the local Sonic and asked for a bag of the peppermints they give out with each order. These peppermints became the nucleus for many of the students models.
You can expand with this project into other models of objects in the universe.