Bet you've never heard of it (I hadn't!) - it gets v little publicity and is not promoted by companies like Uswitch.
Ebico
Same lowish price for everybody for gas including pre-payment meters, quarterly bill-payers and Direct Debits.
Electricity prices vary by region and they are quite green according to this FAQ:
They also do CO2 footprint offsets but I can't get my brain round that yet!
Feature in the Observer today and there are some earlier quotes on their website here .
I have just switched for both