I should not forget to mention my very own website :-). It is a wonderful showcase of how osCommerce's category and products tree can be used for managing content. I tweaked the system by adding many new fields to accomodate the information needed, but the basic structore is still used effectively. A category driven testimonials module has been added as well as a highly distinct module for separating top categories into their own boxes and allowing the insertion of additional information boxes in between that listing.
Excellent SEO very soon after release is a result of finetuning the website carefully. Enjoy!