After evaluating tens of different overly complex e-commerce plugins for WordPress, finding WordPress eStore Plugin was a relief.
It has no payment system integration other than PayPal. There are no product pages, no product images and all other fluff, just the product list, shopping cart, PayPal checkout and digital delivery. The way it works is:
* You create a product record and upload a file to be delivered to the customer
* You create page or post and use WordPress to put any information about product there (product description, images, price, etc)
* You add a small piece of code with your product ID and plugin inserts an Add to Cart button there.
Everything else is taken care of. When your customer completes the payment at PayPal, the file you’ve uploaded, gets emailed to them automatically.