LordPretender

Similar to the original native one, this plugin let you define the range of stats to retrieve. 
Also you will be able to add the category name of the post.
Finally, this widget will only display posts (and not pages too). 
This plugin read the top 100 of posts/pages and keep only the X first POSTS (X = number defined in the widget parameters). So, you can have less posts than requested.
Jetpack is required to work. 
A wordpress account and your blog must be linked.
You can find a demo here : http://www.spoils.fr/ 
The widget is named “Articles populaires” on the sidebar.

Jetpack Popular Posts

Using Jetpack stats, this widget will display the most popular posts.

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.

Jetpack Popular Posts vs Post Views Count (Support caching plugins!)