Energy meters

I'm thinking about getting one of those energy meters that you plug into a socket and then plug the electrical device into the meter......and it tells you how many kwh's it's using.....and some convert that to money if you set the price per kwh.

When we go away, we turn off everything that we can.......leaving just things like the freezer, fridge, alarm and a few other things on. Our usage goes down by about a third while we're away....I suspect the freezer uses a lot but like to find out and also find out what else is using so much when we're home (eg TV on standy).

So......can anyone recommend a good (cheap!) one?