Faster and easier to use than the supermarkets own website, if you've not yet tried mySupermarket.co.uk then give it a go.
You can trim your bill by up to 20% and compare items to ensure you are getting the best possible deal. You can also save 1000s of calories if using the Health Checker which suggests alternatives based on calories, fat, saturated fat, sugar and salt and gives you the option to swap to items which may be better for you. At all times, in the right hand corner of the main toolbar you can view the amount of potential savings still available!
Try them here: mySupermarket.co.uk