Amazon Mobile doesn't let you comparison shop, or identify products that don't happen to be books. But for buying books on Amazon that you find in retail stores, there's nothing better.

is great with groceries and other random products. It scans barcodes only, and tells you where to buy them online and locally. You can read and write reviews. For foods, it even gives you a "nutrition grade."

There's no need to choose between these three apps. They're all great in their own ways, and they're all free. I use them all.

There are other free apps available on both Android and iPhone that read the barcodes of products, then facilitate online purchase. And I'm sure there will be many more to come.

Is it abusive and unethical to shop in old-fashioned stores, find the product you want then buy it online with your phone? Well, that's up to you.