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.

WWW: http://drupal.org/project/ubercart