Re:For an individual device (Score 1)

Kill-A-Watt monitors electric usage for 1 device or one powerstrip. $30 http://www.thinkgeek.com/gadgets/electronic/7657/

The Energy Detective (TED) monitors the entire house. $140 http://www.theenergydetective.com/

I have both of the above. I use Kill-A-Watt for easy analysis of a device and TED for monitoring the turning on/off of major appliances. I also switch the wiring of TED to my generator to monitor it and make sure I don't go over desired load.

Watt's Up Pro is like Kill-A-Watt is for 1 device or one powerstrip but has additional features similar to TED. $120 http://www.thinkgeek.com/gadgets/electronic/7acf/