Fly to is a lightweight jQuery plugin to create add to cart with cool fly effect.
addUI Store is an easy to use jQuery plugin that adds a fully featured store to any website in minutes. The store plugin is written in pure JavaScript (jQuery). PHP is used to secure the store (validate the items' costs / cart's total) and securely process payments.
Minicart is a great way to improve your PayPal shopping cart integration. One simple change and your users will be able to manage their shopping cart directly from your website. Additional APIs provide you the power to customize the behavior to your needs.
Simple Cart is a free and open-source javascript shopping cart that easily integrates with your current website. No Databases, just simple HTML & Javascript with multiple payment gateways options.