Display Products Related To Page Content (wordpress and php)

We use a content api that pulls content into our site via php connect script. The content is parsed and displayed on our site via [login to view URL] file. We would like to show products in the sidebar that are related to the content displayed on these pages. ie: if the page is about fitness, then products for fitness are in the sidebar. I am open to using different ecommerce application, but would suggest Shopp [login to view URL] or WP Eccomerce plugin [login to view URL] as we can assign tags to products. Creative programmer who is knowlegable in wordpress, php, mysql. I think this is "very small" project, but if we decide to add more tasks we can pay more milestones etc.