KOHO - KOHO is a place where you can access your money in real-time and get instant cashback.
Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
Upromise - Upromise is the cashback coupon and rebate site.
Fetchee - Fetchee is a free price tracking wish list app that works with all online stores worldwide.
Paribus - Find out for free if online stores owe you a refund!
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.