Tag Posts Widget is a light widget to show posts from a given set of tag.
Ispired by Category Posts Widget by James Lao – http://jameslao.com
Features:
<ul>
<li>Select any number of tag to be shown.</li>
<li>Add the tag browsed, while browsing the tag archives.</li>
<li>Set how many posts to show.</li>
<li>Option to append the tag names to the title.</li>
<li>Multiple widgets.</li>
</ul>

Tag Posts Widget

Adds a widget that shows the post from a given set of tags.

This Related Posts Plugin for WordPress displays links to a given number of Posts that are related to the current post(s) by Tags or Categories. It can Automatically add links to Related Posts at the bottom of every Post or you can drop the Widget on your sidebar.
Settings: Excluding posts, categories, and tags; section heading; number of links; display post date; and excerpts.

EZ Related Posts Footer Links and Widget

Display a linked list of related Posts by Tags or Categories at the bottom of every post or on the sidebar. Options to show Post Date and Excerpts.

Tag Posts Widget vs EZ Related Posts Footer Links and Widget