Most of the older members use the P4400 (made by P3) as a quick way to measure current amp draw or KWh draw from a single 110 v plug in item. It's great for any 110v charger, but can also give you numbers for any 110V appliance (home theater, computer,etc) that can be plugged into it. Normal pricing is in the $25 range, but it's list is $39.95. It's on sale today for $17.99 plus free shipping. See:
http://www.techbargains.com/news_displayItem.cfm/164474It's a great way to determine some of your actual energy use, and I'll bet you modify your use patterns after you see what some of your appliances cost when "idle."