Released a few days ago, the Market theme for Wordpress allows you to run a storefront on Wordpress. Easy to use with extensive documentation. Plus, additional downloads will be released modifying the theme in different ways, and one download key gives you access to everything, including future upgrades.
Check it out here, as well as a link to a live demo:
http://www.astereostudio.com/revive/showcase/market-for-wordpress-the-theme
Regards!
- aj
Edit: Please note - This is not a free theme