What, When, Where, Watts?

Does anyone know if there is a power supply meter
out there (hardware or software) that would give a power supply readout? If not would it be better to take the current(Amps) reading from the high side or the low side of the power supply?
My thought is the high side would be better, since you actually have current draw inside the power supply and you don't have to work with adapters and such. I might look into making one up and have it give a digital reading onto a meter on the front of the case in wattage. Of course much of this can be done with total calculations from all the hardware inclosed, but with additional fans and drives being added constantly, I think this would be kinda nice to have. Suggestions?