Spray-paint the rind a matte black and let dry. Use a spoon handle to scratch away paint to create stars, moons, and spirals. Add water and blooms. (via Pumpkin Decorating - No Carve Pumpkin Decorating Ideas - Good Housekeeping )
Squeeze one whole lemon and add a tablespoon of baking soda until you make a thick creamy paste. Leave on for up to 20 min, then rinse with cold water. Make sure you make a thick creamy paste. If it's too watery, add more baking soda.
White painted stones by Natasha Newton - These would make a nifty place card. Just hand your guests a business card with a matching design on it. Then they get to match the card to the rock at their place. They could then take the rock home as a keepsake.
*Colored ice balls* Fill balloons with water and add food coloring- red and green would be great around christmas! (be careful not to let the food coloring escape!), once frozen cut the balloons off and voila! Look like giant marbles :)