Here are a few consumer level products for AC 110V power systems:
Efergy’s - Wireless Electricity Monitors - plug load meters
Watts up? - web-enabled electricity controller - plug load meters , at Fry's
TED - The Energy Detective - Montors entire home
Kill A Watt - P3 International Corp. - Monitoring Power Strip
Wattson - DIY KYOTO - This is just a little too cute. For the UK 220v systems.
Conzerv - MeterCenter - Montors entire home, also industrial meters.
Measurlogic Inc. - Socket Energy Meters - Makes many industrial meters.
Some of these are "plug load" meters, this measure the amount of electricity used by whatever is plugged into them.
And products for DC systems: