required modules to develop a ecommerce website
For Drupal, it's Drupal Commerce that worth consideration now. I worked with it couple of months ago, it takes some time to get used to it, but once you get it, you can create a lots of things with contrib modules and other tools that you can't do without custom development with other CMS.

You will find lots of how-tos, contrib modules and other informations about Commerce http://www.drupalcommerce.org/

Also make sure to check out Commerce Kickstart, which is an installation profile for Drupal stores and it's coming with basic configurations like set up product - product display, and it contains all required modules and dependencies for Commerce http://drupal.org/project/commerce_kickstart