Kill-A-Watt

Think Geek:

The Kill-A-Watt allows you to connect your appliances and assess how efficient they are. A large LCD display counts consumption by the Kilowatt-hour, just like utility companies. You can figure out your electrical expenses by the hour, day, week, month, even an entire year. Monitor the quality of your power by displaying Voltage, Line Frequency, and Power Factor.

$29.99.

Photo by thinkgeek.