Fluff In Your Clothes Dryer
Old tennis balls can be used in your drying machine to help fluff around your clothes. The tennis balls allow more air to pass over your clothes. Essentially, this helps lessen your dryer running time. You can also use tennis balls in your dryer for blankets or pillows with feathers, as it helps prevent them from lumping together.

Cover For Towbar On Cars
An old tennis ball makes a very good cover for a towbar ball to stop it rusting. Simply make a cut on one side of the tennis ball and then slide it over the towbar ball.

Tennis Speaker Feet
Take 2 old tennis balls and cut them in half. Place each half under the 4 corners of the speakers and they act as vibration isolation. You can also paint them black to make them blend in.

Rubber Feet For Childrens Chairs
If you split a tennis ball and then place them on the bottom of the metal chair legs in classroom at junior school, this has the effect of cutting down the amount of noise made as the chairs are dragged across the floor.

Garden Slug Collectors
By cutting a tennis ball into two halves you can create excellent slug collectors. Leave the two tennis ball in strategic locations around your garden and then collect the slugs that end up inside them. You can then feed the slugs to your local bird population.