My favorite is the
Mooshimeter, a Bluetooth dual channel multimeter. I got it since it doesn't have a rotary switch to wear out or get dirty (that's a very common problem I have with multimeters - I use them a lot), plus it can operate as a standalone data logger and even works as a (very low frequency) oscilloscope.
Of most interest to us here is that it can measure power to a far greater precision than a Kill-a-Watt. The 30mW an idle phone charger uses is easily captured. They're working on (software) support for an external shunt, which would be great for checking power usage of devices that draw too much current for its internal shunt.