LoveSales - Find and save products you love, get alerted when they go on sale.
Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
TrackIf - Alerts you if the price of your favorite products drop
Paribus - Find out for free if online stores owe you a refund!
Giftwhale - Giftwhale allows you to create personalised wish lists online.
Savelist - Found products you want but not ready to buy?