Ubercart
Ubercart is an e-commerce suite developed for Drupal. It has been designed with the end user in mind, focusing on usability in three key areas: store configuration, product and catalog creation, and order administration. On the front end, all major systems are configurable and integrate with the standard Drupal systems (node, taxonomy, user, etc.). On the back end, the settings pages and order administration pages have been designed with ease of use in mind, and we are constantly working to lower the barrier to entry for new Ubercart users.

UC Node Checkout:
This module allows you to map a node type to an Ubercart product. When a user creates a node of that type, the specified product is added to the shopping cart with a node reference to the newly created node. Options in the module allow you to turn links in the shopping cart into edit links for the node, display a summary of the node details in the shopping cart and on the order screens, and hide CCK fields on the node type from users who don't have the "edit content" permission. This makes the module an ideal candidate for registration site and customizable product sites that contain additional fields only administrators should have access to when processing the orders.

http://drupal.org/project/uc_node_checkout