AndrewUlrich

This plugin creates two widgets:
<ol>
<li>A widget where you can choose from all the categories in your blog.</li>
</ol>
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.
<ol>
<li>A widget where you can choose from all the tags in your blog</li>
</ol>
You can select the tags you want to search for, and it will only show posts that have all of the tags you selected.
<h3>Known Issues</h3>
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.
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.

Faceted Search

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

Prasanna SP

This plugin creates a new widget which lets you show a list of recent posts based on categories or tags. This is a must have plugin if you want to exclude some categories in recent posts widget or if you want to show recent posts based on tags. By default the wordpress recent posts widget shows a posts from all category. But this plugin gives you more power to customize your recent posts widget. You can also display post date in the widget.
See the live action of this plugin on <a href="http://demo.prasannasp.net/custom-recent-posts-widget/" rel="nofollow ugc">demo site</a> or on Kennneth John Odle’s <a href="http://blog.kjodle.net/" rel="nofollow ugc">blog</a>.
Have any questions or suggestions? Create a thread in the <a href="http://forum.prasannasp.net/forum/plugin-support/custom-recent-posts-widget/" rel="nofollow ugc">support forum</a>.
Visit <a href="http://www.prasannasp.net/wordpress-plugins/" rel="nofollow ugc">this page</a> for more WordPress Plugins from the developer.
A special thanks to <a href="http://blog.kjodle.net/" rel="nofollow ugc">Ken</a> and <a href="http://www.joshlobe.com" rel="nofollow ugc">Josh</a> for testing the code.

Custom Recent Posts Widget

A widget to show recent posts list based on categories or tags

Faceted Search vs Custom Recent Posts Widget