Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.
ZXing - Barcode Scanner for Android
Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
QuickMark - QuickMark makes everything possible.
Shopping.com - Shopping.com is a leading price comparison site that allows you shop online for the best deals and lowest prices. You can read unbiased product reviews and compare prices online. Online shopping has never been as easy!
QR Droid - QR Droid Zapper