Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
PriceSpy - PriceSpy helps you save money when shopping online.
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.
Yahoo Shopping - Yahoo Shopping’s price comparison website is similar to Google Shopping. Store owners can add their products to the platform. You’ll find products sold by brands like Walmart and Amazon on the platform.
Reprice Tracker App - Simple and beautiful Amazon price tracker
Google Shopping - Find the best products, prices and places to buy