The mention in the hdd thread of "power saving" got me thinking about how much power my computers use. I know that they must use a fair bit and cost a significant amount to run, but I don't know how much or how to measure it.

Ideally what I want is something I can plug into the mains between the device I am measuring and the supply. Maplins at one point sold something like this, but I made the mistake of not buying one at the time. It was perfect because it could also calculate the cost of the power being used.

They don't appear to sell anything like it anymore, nor can I find anything similar. The Maplins device was made by a German company, whose name I have forgotten.

Is there such a device out there still and if not is there an easy way of measuring power use over time ?

Edit: oh yes, forgot to say it needs to work on the UK mains supply