I've never implemented a shopping cart within a Wordpress site and I'm a little overwhelmed with the number of ecommerce plugins out there. I have an existing gallery of products and I'm simply looking for a simple solution to add a "add to cart" button below my images and a "checkout" button where user can make payments. I've tested out a few plugins, but haven't found one I can get working and were not easy to get set up. I'm wasting far too much time searching for a good plugin for my needs, so I'm hoping someone can suggest a good one.

Any recommendations? (and ideally this would be a free plugin).