I’ve wanted one for ages, and finally decided I had to have one. Loads of research, 11 phone calls and a dozen websites later, I’ve taken delivery of a P3 Kill A Watt wattmeter. (And 2 of my co-workers ordered them from the same place directly afterward :P).
After making up a spreadsheet and testing almost everything in the house, I’ve so far discovered that at 10c/kWh, my refrigerator is costing me ~33$/year, my freezer 39, and my computer (which I knew to be a large drain and am replacing shortly) just over $200.
Interestingly, the HP 6110 all-in-one that I scrounged from a repair pile at the office and just use for occasional scanning draws a constant 8 watts (7$/year) even when it's turned off. That got unplugged right away, though the [unexpectedly low](http://boards.straightdope.com/sdmb/showthread.php?t=432641) 2 cents/load on my washer is still a mystery to me. Anyhow, you can't borrow it 'cause I'm not done with it and have 3 people already lined up, but if you check your library, they might loan you one. :)