Shopp is an e-commerce plugin that adds a feature-rich online store to your WordPress-powered website or blog. Get your store up and running in minutes. Then, take it to the next level with the flexibility of Shopp’s customization tools that allow production studios and power users to tailor every aspect of the shopping experience.

Shopp looks and works like it was meant to be part of WordPress all along. With support for SSL security, transaction information is encrypted during processing and no credit card information is stored on your website to ensure your shoppers’ safety.

Pricing: Single ($55), Developer ($299)
Requirements: WordPress 2.8
Source: http://shopplugin.net/