Here’s an excellent WordPress plugin for sites that have a lot of categories and tags for posts. You can use Taxonomy Drill-Down to either a widget on the sidebar which displays a faceted search box. The widget shows plus and minus signs for categories/tags, allow your visitor to drill down to a filtered set of posts matching their criteria.
It even supports the Simple Taxonomies plugin (similar to post types) so you can do even more fancy things.
You can even use the plugin to insert code snippet directly into your theme template to show it anywhere on your WordPress site.
Based on our experiences, here are some tips: before you install this into a live WordPress site, install this into a test WP site where you have a recent copy of your content imported. Once you actually test out this plugin yourself, it will expose any deficiencies in the way you’ve set up categories and tags. In our case it showed we went a little overboard setting up categories on some of our sites. The plugin also automatically loads new matching posts on the fly so there’s a quick transition that jumps the user to a new page so the widget disappears below the fold making it somewhat jolting, so you may want to have this widget near the top of the page so the user doesn’t wonder what just happened when they use it.
You can use this Taxonomy Drill Down plugin in combination with an improved search plugin like Relevanssi to help your visitors find the content they’re looking for. After all, if you have a ton of useful content you should make it easy for people to find what they’re looking for.
Get it: Taxonomy Drill-Down plugin