I have just had delivery of an Eco-Eye Mini electricity consumption monitor, and I'm very impressed.
The monitor is easy to install, just insert the batteries and clip the sensor wire around the live wire in your electricity meter cupboard. You then have a very clear read-out of your current electricity consumption in KW. You can enter the current price per unit for your electricity, and the monitor will then also be able to display the current cost per hour (or day, week, month, or year).
The monitor's output has a resolution of 10 watts, so you can see the effect of turning lights on and off, even low-energy ones.
The range of the monitor is reasonable. In our house with solid internal walls it works in most places apart from the furthest points from the transmitter. The range seems similar to that of our Speedtouch 585 v6 wireless router.
The Eco-Eye is made in the UK, and much more information about the unit is available from the manufacturer's web site: http://www.eco-eye.com
The unit is competitively priced too, and if you order from the Good Energy Shop soon you can get a 25% discount, making the monitor £33.94 including postage.
Later in the summer there should be a USB-interfacing receiver available too, with battery backup and data retention for when your computer is switched off. This listens to the same radio signals as the standard monitors, so will work nicely in parallel. Should make analysing trends in household electricity usage easy.