Ivan Storck

The <a href="http://www.sustainablewebsites.com" rel="nofollow ugc">Sustainable Websites</a> WordPress Subcategories Widget displays all subcategories on a WordPress category archive page.
The widget will not show un-necessarily on pages or posts.
This widget is a useful navigation feature that will help your web site visitors drill down into your category hierarchy to find the right category. It is completely style-able with CSS. It’s also good for search engine optimization (SEO) to help your site’s link structure be easily crawl-able.
It’s a simple widget that does exactly what it says! Drag to your sidebar to activate.
Plugin homepage: <a href="http://www.sustainablewebsites.com/wordpress-subcategories-widget" rel="nofollow ugc">WordPress Subcategories Widget</a>
If you have any suggestions please email wordpress (at) sustainablewebsites (dot) com

SustainableWebsites WordPress Subcategories Widget

This WordPress Subcategories Widget displays all subcategories on a WordPress category archive page.

Marios Alexandrou

DigitalME

As the name suggests this plugin will completely remove the mandatory ‘Category Base’ from your category permalinks ( e.g. ‘mysite.com/category/my-category/’ to ‘mysite.com/my-category/’ ).
The plugin requires no setup or modifying core wordpress files and will not break any links. It will also take care of redirecting your old category links to the new ones.
<h4>Features</h4>
<ol>
<li>Better and logical permalinks like ‘mysite.com/my-category/’ and ‘mysite.com/my-category/my-post/’.</li>
<li>Simple plugin – barely adds any overhead.</li>
<li>Works out of the box – no setup needed.</li>
<li>No need to modify WordPress files.</li>
<li>Doesn’t require other plugins to work.</li>
<li>Compatible with sitemap plugins.</li>
<li>Compatible with WPML.</li>
<li>Works with multiple sub-categories.</li>
<li>Works with WordPress Multisite.</li>
<li>Redirects old category permalinks to the new ones (301 redirect, good for SEO).</li>
</ol>

No Category Base (WPML)

This plugin removes the mandatory 'Category Base' from your category permalinks. It's compatible with WPML.

SustainableWebsites WordPress Subcategories Widget vs No Category Base (WPML)