AndrewUlrich

<p>This plugin creates two widgets:</p>
<ol>
<li>A widget where you can choose from all the categories in your blog.</li>
</ol>
<p>This is similar to what newegg.com uses, where you can select multiple categories, and it will only show posts belonging to all the categories you select, and such categories can be narrowed down by selecting their subcategories.</p>
<ol>
<li>A widget where you can choose from all the tags in your blog</li>
</ol>
<p>You can select the tags you want to search for, and it will only show posts that have all of the tags you selected.</p>
<h3>Known Issues</h3>
<p>After upgrading from 2.1 to 2.2 it is highly recommended that you deactivate the plugin and then re-activate it.  Unfortunately WordPress 3.1 no longer calls register_activation_hook when the plugins are upgraded, so this may be necessary, otherwise you may not see all your categories.</p>
<p>When using version 3.2 or above, and excluding categories, the display order may or may not be mixed up when you exclude a parent category.</p>


Faceted Search

This plugin will create widgets that you can use to conduct faceted searches using the categories or tags on your site.

tugbucket

<p>Multi-column Tag Map displays a columnized and alphabetical (English) listing of all tags, categories, authors, pages, posts, single custom post types or taxonomies used in your site similar to the index page of a book. This makes it easier for your visitors to quickly search for topics that might intrest them. It’s a great alternative to the tag cloud and especially useful if you have a large site with a multitude of subjects, products etc…</p>
<p><strong>Live examples and option details can be found at <a href="http://mctagmap.tugbucket.net/" rel="nofollow ugc">mctagmap.tugbucket.net</a></strong></p>
<h4>Features</h4>
<ul>
<li>Alphabetically lists tags, pages, posts, categories, custom post types, authors and taxonomies</li>
<li>Over 50 customizable options</li>
</ul>
<h4>Links</h4>
<ul>
<li><a href="https://mctagmap.tugbucket.net/" rel="nofollow ugc">Options and Documentation</a></li>
<li><a href="https://wordpress.org/support/plugin/multi-column-tag-map//" rel="ugc">Support</a></li>
</ul>


Multi-column Tag Map

Multi-column Tag Map will display tags, pages, posts, categories, custom post types, authors and taxonomies in a visually logical way similiar to that …

Faceted Search vs Multi-column Tag Map