http://ninjablocks.com/
All code is Open Source (https://github.com/ninjablocks/) and very very hackable (it is all beaglebone/RPI/Arduino based): http://ninjablocks.com/blogs/how-to/750 ... ur-arduino
Sensors/actuators use 433mhz, thus we might be able to get RFXCom to talk to that (RFXCOM: Hint hint hint!

Prices seem quite lowish too for their actuators/sensors:
http://ninjablocks.com/collections/actu ... ocket-type
Power socket (EU): 10 USD
http://ninjablocks.com/collections/sensors
Motion Sensor: 15 USD
Temp/Humidity: 15 USD
Window/Door Contact 6 USD
and there is a whole list of compatible things:
http://wiki.ninjablocks.com/devices?type=sensor
http://wiki.ninjablocks.com/devices?type=actuator
The latter lists KAKU too btw, and as they do 433mhz, I guess most other toys in that range are compatible.