Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
Gift Hero - The best wish list ever
Fetchee - Fetchee is a free price tracking wish list app that works with all online stores worldwide.
Coupofy - Coupofy is USAs number 1 trustworthy deals and coupons website.
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.
LoveSales - Find and save products you love, get alerted when they go on sale.