Most of you are Internet savvy - otherwise you wouldn't be using this forum - so I am sure you've heard of them before. But for those who haven't, try the following:
Use them with a pinch of salt, but they can help you locate the cheapest price for a particular item. There are more of these about too, so it pays to do some googling. Last of all, don't use credit cards! They are the spawn of satan. Spend money that is ACTUALLY yours!