MySupermarket.co.uk is another useful site well worth checking out if you intend to do shopping online, it compares your shopping list for one online supermarket with that of 3 more. The supermarkets MySupermarket checks out include Tesco, Ocado (Waitrose), ASDA and Sainsbury. It allows you to checkout which supermarket it is actually overall cheapest to buy all your shopping from, allowing you to save money on your food bills!
One extra benefit is that as well as receiving your Nectar and Clubcard points you can also receive ipoints for shopping through MySupermarket as well. The only disappoint I had with MySupermarket is that 4 supermarkets is missing out on many more on the high street, but I guess this would become quite had to do and would reduce whatever incentive MySupermarket may have for sending custom to one of the online stores!
External Link: mySupermarket