freetools

LMP allows you to add in your sidebar a widget that will display the last modified articles in descending order of modification date.
Settings to customize:
<ul>
<li>Allow you to set title widget</li>
<li>Display Number of items</li>
<li>Display modified date</li>
<li>Display thumbnails</li>
</ul>
If no thumbnail was found for the article, LMP will add a generic image.

Last Modified Posts

Add a widget to display the list of the last modified/updated posts.

This plugin is not for most WordPress users. It will stop WordPress from automatically updating witch is not recommended. The only reason you might need this plugin is if you have modified your WordPress core files and you want WordPress to stop overwriting them with their automatic security updates. Otherwise you should probably just let WordPress auto update.
Updated April-19th

Stop Auto Updating Dangit

This plugin simply stop WordPress from automatically updating for you.

Last Modified Posts vs Stop Auto Updating Dangit