If only there was an website where you could say, for instance: "I'm going to Sainsbury's, I want a white wine, and I don't want to spend more than a fiver. What's the best wine for my money?"
There is such a website: Malcolm Gluck's Superplonk. Tell it which retailer you're going to, what style of wine you're looking for, how much you want to spend, and up it pops with loads of recommendations. The wines are listed in the order of the score they recieved from Mr Gluck when he reviewed them.
The only difficulty is remembering the name of the wine when you get to the store and are confronted by thousands of choices. I need a PDA!