Tennis balls have many more uses than simply hitting them back and forth on the court, or tossing them for your dog to chase.
For instance, dryer sheets are expensive even though they are effective at removing static from laundry, but a tennis ball wrapped in aluminum foil will do the same thing, and it is more than single-use.
The foil reduces static while the ball bounces around during the cycle.
A brand new tennis ball is also perfect for removing unsightly black streak marks on tile and linoleum surfaces. Try sticking the ball to the end of a broom handle by cutting an X in the surface so you can use the trick on your feet.
Curtain rods can be made more ornate with the addition of a tennis ball wrapped in fabric and stuck on the end of the rod. Tennis balls also make a great pool-cleaning tool. Simply throw the ball in the water and let it float around the surface for several days.
The new tennis ball will pick up oil and debris that skims the surface. This makes cleaning the pool much easier, and it puts less strain on your filtration system.
Tennis balls make great coin purses as well. Simply cut along the edge of the ball so that it can be squeezed open.
Since the balls are hollow but hold their shape, they can hold change, paperclips, rubber bands, or anything else that might clutter up a purse. You can also use a hanging tennis ball to mark the stopping point for your car in the garage.