customizable shopping cart

A shopping cart that is can be custom designed to one of many websites that I look at creating in the future. Would need to have a backend section to so I can easily add new products to site at my choosing etc And advice on what type of merchants available to interact into site, must have min credit card payments (even if I get my own to interact into site) ## Deliverables the template isn't complete, but will provide the basis on what we are after, there is about 5 other pages, and the shopping side can come from anyoneof these pages, and need to intergrate into the shopping cart. the final shopping cart will need look like this site for payment etc