There is an osCommerce add-on called Next-Previous ([url removed, login to view]) which allows for easily switching between products within a given category or manufacturer on the product_info level.
However, there is a problem with cloned products.
When there is a cloned product within a given category which has its root in another category, next-previous switches to the other (root) category and continues its next-previous journey in that category.
Furthermore, there is a contribution called Product Specifications ([url removed, login to view]) which allows for filtering products. When you go from the filtered product listing to one of the products, next-previous switches between the products within the category of that products and not between the products of the filtered product listing.
In short, we would like to have a (filtered) product listing array before going in to [url removed, login to view] so that next-previous switching takes places within the (filtered) product listing and not in a newly defined but sometimes unrelated products listing array.