Specific Shopping Cart Plugin

In my business I sell digital stock illustrations for each of my artists. Would appreciate if someone would suggest the best plugin to allow me to sell digital illustrations that the customer would pay for using Google Checkout, Paypal or CC to download 300dpi files to their desktop. Would like to see a grid layout on page with tags and categories to allow customer to search stock site and no monthly fee’s. Looking for a flat rate, one time fee to purchase plugin. The site I have in the works is located at: http://thewileygroup.com/wordpress/

Thanks in advance for any suggestions. David