I posted a link to the Tweet-a-Watt which is exactly this. If you don't need computerized monitoring, you can just buy a plain Kill-a-Watt at your local hardware store for $20. I use it on my AC and find it quite helpful.
Actually - the two companies I linked are exciting because they can do device-level monitoring with just a single monitoring device at the meter.
Both companies do a horrible job of explaining this on their website, but one of my coworkers went to a presentation they were both at the other week.
Basically, they have a database of unique waveforms(?) (I'm an electrical illiterate, so I may be saying something quite stupid) for individual devices and appliances. So, for example, when you plug in MacBook Air to recharge it, they know the unique profile of the effect that device will have on your home or office's power consumption, so they can separate it from your overall power draw.
Which means that the software, using a single measurement point, can break down your home or office's entire energy consumption by individual device / appliance in realtime.
Which to me, seems a bit mind-blowing. But like I said, both companies do a horrible job of explaining this on their websites.
