The Invisible Hand addon for Firefox is a cool shopping assistant which constantly scours the net for cheaper pricing on the product you’re viewing at any time. It’s not the only tool of its kind, but the devs have made it nicely discreet which makes it more acceptable than most.

The software copes with 50 stores in the UK and USA, so it’s worth installing just to make sure you’re getting the best deal. Of course one of the things that things like this don’t tell you is how good the support, returns policy, delivery etc is from the cheapest shop, all of which can be even more important than price. So basically, don’t stop your due diligence just because you’re saving a twenty on the deal, right?