How to add a filter option
 

I was wondering how to provide filter options in the final product listing screen. Let's say: how to filter the final product listing by brand name (filter options to be given as a drop down list which includes all brand names appearing in the current/active product listing).

This is possible using the advanced search mechanism. If you look at the code for the advanced search template and use that as the bones for the filter system it should point you in the right direction.

Just have things like the category as a hidden field rather than the drop down in the form.