Hi,
I bought one of these Ryobi power monitor units at Home Depot -- about $25(?).
Power Usage Meter by Ryobi
I like it because it retains the values it measures even after you unplug it from the wall -- it has an internal battery. Also easy to use.
BUT, it appears to cut out with not very large loads. If I plug my efficient fridge into it, it will cut out -- apparently it thinks the load is too high. It resets itself after a few minutes. The regular KillAWatt meter has no problem with the fridge.
The Belkin unit posted above looks like it might be a good bet.
Gary