Although it's not often used in nonprofit settings, the Drupal module (or, more correctly, a large suite of modules) called "Ubercart" is a pretty amazing tool if you need to create a shopping cart system. We've implemented it for organizations that want to sell fees for events, sell items, and take donations. It doesn't have many of the strengths of CiviCRM, but it has a lot of useful features if you want to sell things, or combine selling things with taking donations, memberships and selling event tickets. A while back, I'd heard of the Ubercore initiative - a group of developers working to bring Ubercart to Drupal 7 (there was quite a delay between the release of Drupal 6 and the availability of Ubercart for Drupal 6.)  That initiative is now called "Drupal Commerce. (other site here.)" It is basically meant to be a rewrite of Ubercart for Drupal 7. It looks to be something to watch. Gregory Heller of CivicActions wrote an interesting conceptual piece on the integration of Drupal Commerce and CiviCRM that's worth a read. (By the way, there is a module done by DharmaTech that integrates CiviCRM and the current Ubercart.)