If you have had trouble getting your cat to drop his or her friends off at the pool rather than the sand box, CityKitty may be the solution for you. Consisting of a series of rings that are removed from a mock toilet seat as your cat grows used to the idea, the CityKitty provides a (supposedly) simple, low-cost way of training Fluffy to use the john. Now to train the cat to flush.
CityKitty, Potty Training for Your Cat That Works [OhGizmo!]