When I first started working on home power monitoring, nothing existed for homeowners to understand and manage their home power consumption.
I found this home energy monitoring website, which has been around for awhile now: http://www.kondra.com/circuit/circuit.html
His power usage display is spectacular: http://www.kondra.com/circuit/images/panelhist1.gif However, I priced out the components he used, and his Veris A/D converter runs about $1500 last time I checked. Way, way beyond the cost of the elegant Arduino.
Trystan Lea's site is where I first found Arduino and how it can be used for power measurement: http://openenergymonitor.org/emon/
The name of this blog, "openwattmonitor", is meant to show the lineage, as the child of openenergymonitor.org.
"The OpenEnergyMonitor project is based on the work of two developers, Trystan Lea and Suneil, both from Wales. "This is a project to develop and build open source energy monitoring and analysis tools for energy efficiency and distributed renewable microgeneration." The project appears to have been launched in the summer of 2009."
It's all happening now, in real time. They have visualized an "energy monitoring and management framework" that encompasses both open hardware and open software in innovative ways I've seen nowhere else and mobilized an impressive force of technical ability to make it happen.
Dave's "Desert Home" blog blazes new trails in measurement of home power usage in the US, and with interfacing the output to Pachube at pachube.com:
Dave's writings describe how he started measuring his home energy consumption and caught his local power company overcharging him. After calling them on it, they replaced the meter and his power bill was affected very favorably.
I bought my stuff from SparkFun: http://www.sparkfun.com/
Home power monitoring is here to stay.