Recomendation for simple cart integration into custom site

I would like to know if there is a simple way to integrate a shopping cart experience into a custom site, who's front end I develop myself. I am experienced with front end design, HTML, CSS, jquery, but have only a moderate amount of experience with server side scripting.

So far the options I've looked into, such as zencart, are full-fledged CMS systems that take control over everything, including the front end. While I don't wish to create an entire cart / store system myself (with my limited server-side knowledge), I would like to know if there is a relatively light system I could integrate into my site, that controls the cart / purchasing functions. All while I control the front end design on my own terms.