Acquia Prosper is a classic free ecommerce Drupal theme created by TopNotchThemes. With a monochromatic look and clean lines, it is designed as an Ubercart e-commerce theme that is easy to customize, but is also extremely flexible for any type of website. Acquia Prosper is compatible with Drupal 6 & 7.
AT Commerce is a Drupal theme created specifically for Ecommerce sites with built in support for the Drupal Commerce module and Ubercart. It has a responsive design which means that it will work well on most mobile devices without any additional effort. This Drupal Ecommerce theme has support for 26 regions, color module, custom login block and a superfish menu. AT-Commerce also supports a slideshow, slide-down top draw and Google fonts. There are options for changing the settings of the image field alignment, menu bullet and background texture overlay and it also supports Calendar and Quicktabs.
Storefront is a Drupal Ecommerce theme that was designed to work along with the Drupal Commerce module. Storefront has features like Commerce specific templates, responsive techniques using media queries, cleaning up of form elements specific to cart and checkout panes, 960 proportioned fluid width with option for setting fixed width and theme settings for setting colors layout options, site framing and home grids.
Metropolis is a tableless Drupal theme which supports a 1 or 2 column layout. with 10 collapsible block regions. It has a superfish drop down menu and an image slideshow plus it provides an option for custom login and logout. Metropolis can be used with Ecommerce websites as well as personal and corporate websites.
Velvet Sky has been specifically built for Drupal Ecommerce sites. It has been ported from Wordpress and is based on the Lightweight Drupal theme.
I hope this list helps the next person looking to fit Drupal Commerce with an awesome theme! Feel free to post your Drupal Commerce themes in the comments.