Julio Potier

IMPORTANT: 3.0 supports cahing plugins!
When someone visits a post or page (not a search engine bot crawler), it adds 1 count views to its counter.
But this is not all, the counters are split in days, weeks, months, years, so you can see stats and display any stat day.
Then you can display this views with the provided shortcode [post_view] or use the widget to display a top (or less) posts list.
You can also use [most_view] in a post/page to get a top (or less) post most viewed.
If you were using another kind of plugin before and don’t want to lose your counters, this plugin can keep them!

Post Views Count (Support caching plugins!)

This plugin counts views for post and pages, shortcodes [post_view] & [most_view] are available, also a widget "Most Viewed Posts" is.

Nader

The “Most Comments” plugin displays as the name says posts with the most comments. You can either use the widget in the sidebar or integrate the plugin as template tag in your theme files.
Features:
<ul>
<li>Limit the amount of posts to be shown</li>
<li>Show comments from a specific post category</li>
<li>Exlude posts without comments</li>
<li>Select a time range (last XX days) of posts to be taken into account</li>
<li>Customize the design template via the settings page</li>
<li>Place a widget in your sidebar</li>
</ul>
More Information & Feature Description: 
http://www.brandinfection.com/wordpress-plugins/most-comments/
<h3>Configuration</h3>
You can configure the most comments plugin to your needs. Options can be found under the menu <code>Settings > Most Comments</code>

Most Comments

Display posts with the most comments, as a widget or on a page using the template tag. Customize the look with specific settings.

Post Views Count (Support caching plugins!) vs Most Comments