Cart66 is the best WordPress plugin when it comes to security. It does the job for you so you can concentrate on the revenue generating aspects. It provides a built-in recurring billing engine that works perfectly with any payment system, an email center to send follow-up newsletters, and online magazine subscriptions. You can even sell music on WordPress.
This plugin allows you to easily install the shopping cart without which no e-commerce website can survive. You can download the software on your Desktop, PC, Mac, iPad and Android to manage your cart wherever you are. It supports any popular payment system, you can set 7 different languages on it, set up coupons and promotions, integrate Google Analytics.