Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
Auction Price Finder - Check the current value of any item on ebay, based on the last sales.
GlassIt.co - Find discounts, without invasion of your privacy. Download Glass It Price Tracker mobile app or browser extension 🇺🇸
Altosight - eCommerce price monitoring & tracking software
Pricy - Amazon price watch
Bidvoy - Bidvoy is an effective product value tracking service for eBay that is providing complete requirements as far as auctions are concerned.