Efergy e2 Wireless Electricity Monitor
The e2 is a wireless electricity monitor for your household. It allows you to see your electricity usage on your computer, and track your carbon footprint. Energy usage is displayed in kilowatt hours, as would be shown on your bill, and by inputting your local rate, can be shown as expected price. Seeing instant usage allows you to see the effects of turning on and off lights, unplugging unused devices, and lets you get instant feedback on your energy usage.
It is sold in the UK; it is unclear if it works outside the UK.