iPhone has introduced the first accurate bar code scanner in an app called Red Laser.  It works with UPC and EAN bar codes.  Red Laser allows you to scan the bar code of any product and find the places online that offer the best prices.  You can keep a list of all your scanned items or place them on a grocery list.  You can even read reviews for books and movies that you scan to see if you want to buy them.  This is the direction that comparative shopping is moving in: making everything simpler.

Demonstration video for Red Laser: RedLaser Demo