Nintendo announced at their E3 2007 press event (still going on, watch here)Mario Kart for Wii and the Wii Wheel.

Mario Kart for Wii will feature online gaming. Nintendo's Reggie did not reveal how many players can drive against each other online.

Mario Kart for Wii is not coming this Holiday season. It will be released in early 2008. The Wii Wheel looks neat, but there are already other 3rd party Wii wheels out there. So it is nothing really unique.
Nintendo also announced today the Wii Zapper, which resambles a machine gun. It carries the Wiiremote and the Nunchuck together.

More E3 2007 News.