Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
LoveSales - Find and save products you love, get alerted when they go on sale.
Fetchee - Fetchee is a free price tracking wish list app that works with all online stores worldwide.
TrackIf - Alerts you if the price of your favorite products drop
Savelist - Found products you want but not ready to buy?
Giftwhale - Giftwhale allows you to create personalised wish lists online.