Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
QuickMark - QuickMark makes everything possible.
Fetchee - Fetchee is a free price tracking wish list app that works with all online stores worldwide.
ZXing - Barcode Scanner for Android
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.
Barcode & QR Code Scanner - A free app which allow to read and generate barcodes for Android.