Note: I used the xbee I linked to, but for a one to one communication, rather than a network of wireless devices, xbee series 1 would do fine, but the AT commands are slightly different.
This instructables was made at TechShop! www.techshop.ws
You can also control servo motors, or make a moving wireless security camera, as seen below.
In the photos I'm actually using an seeeduino but it is very similar to Arduino