Usually I do constant research on projects to automatize things at home, like energy monitor. Long time ago I came across this little nice post, explaining in a very simple way how to monitor your home energy consumption. On top of that he is using an ethernet shield that outputs the information through a MQTT feed to xively.com where it is processed and transformed in a nice bar graph.
UPDATE: Xively is not free anymore so this example will not work. Soon I will post an alternative using other types of logging.
UPDATE2: Here you can check another project using sparkfun server and thingspeak server