An alternative to the Belkin Wemo could be the Z-Wave outlet :
The outlet is $50, or the Lamp Module which is similar to the Wemo is also $50.
There are a whole bunch of useful Z-Wave products :
I guess there would need to be a Z-Wave Shield to be able to communicate with the devices since it is not Wi-Fi.
Continuing the discussion from Controlling Belkin Wemo from Spark Core: