If you are an npower customer and haven't changed your dual fuel tariff in a while, probably worth doing so. Most people probably know this, but they are always adding new offers that you won't be offered as an existing customer. You have to go online and make the change yourself. They won't let you do it by phone, even if you ask. It takes a few minutes but can save quite a lot. The current best deal (for me in this area anyway) is Sign Online 13 - Electricity & Gas - If you are on an earlier version you will probably save. I've just shaved an est. £125 off my annual bill. Give it a go if they are the cheapest supplier in your area already and save even more - link on the next post.
I'm a new customer so it won't affect the date that the £100 dual fuel bonus is awarded (after 12 months), but you might want to check your own situation by giving them a call first so as not to lose out on this. Not even sure if it does mean a new contract or the tariff changes and the bonus stays. 0800 028 4361 for more info