The LiveMove product was announced by AiLive yesterday. You can use your own gestures to create a gesture-based game. Here is a demonstration video (also available at google video). Unfortunately it costs $2500 a pop, on top of the $2000 or so it costs to get a Wii developer license. As an alternative, you can use the XNA framework for .NET and XBox 360 development for about $99, but of course the XBox costs more than the Wii will.