Having just signed up to Ecotricity, this risks being tainted by a certain smugness, feeling a bit pleased about 'doing my bit' to reduce my carbon footprint. However, the intention is to praise a company worth its weight in ... um, carbon. If you haven't been put off by the Climategate email scandal and if you want to reduce your carbon footprint, check them out.
Firstly, it is easy to switch. You can either apply through the site OR (as I did) go to the Green Electricity Marketplace website. You can compare different tariffs, green-star ratings and ROCs. The switch is done between current provider and Ecotricity and all I've had to do is ask for my final bill and provide an up-to-date meter reading.