Taxonomy Sifter is a Drupal module that provides a block with terms which any or all selected must apply to a node for it to be listed when viewing a taxonomy term page, e.g.
taxonomy/term/... The vocabularies used in the block is configurable.
Read the module's handbook page for more information.
Yes, we finally have 6.x support! It also come with a new feature: Ability to format the sifter links as Select list, checkboxes, or buttons.
The button feature has only been checked with two vocabularies, and may only work with two. Please help out by testing it.