Categories; feature request or advice needed

I will be using many categories, sub, and sub-sub categories. As they get identified by the authors they trail down the sidebar in a huge list. Can this list be made collapsible to the parent category? It would be very tidy and just as usable. Also, as categories get posted along the top of the page, can they be made to ‘stay’ when clicked so that a user has a chance to read them? They flick off too quickly. Thanks. Leslie