We haven’t…uh…tried this yet (primarily because Cult editor Leander Kahney refuses to get back into his fencing Mexican-wrestler costume after last year’s Halloween fiasco) but it looks pretty damn cool, or something.
Sonic Speed Ball sets up a Bluetooth connection between two iPhones (or BT-equipped iPods), then simulates a virtual ball that can be smacked around using an iDevice as a paddle. Different gestures affect the virtual ball in different ways, à la the Nintendi Wii controller.
Sonic Speed Ball is $1; leash not included.