Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
Chart.js - Easy, object oriented client side graphs for designers and developers.
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.
D3.js - D3.js is a JavaScript library for manipulating documents based on data. D3 helps you bring data to life using HTML, SVG, and CSS.
Fetchee - Fetchee is a free price tracking wish list app that works with all online stores worldwide.
Google Charts - Interactive charts for browsers and mobile devices.