cpjolicoeur

Category Teaser uses a WordPress widget to display the latest post excerpt from a category you choose. The output can be styled using CSS.

Category Teaser

Displays the excerpt from the latest post in a certain category with link to full post

javierjara

This plugin adds a simple widget that you can customize easily it allows you to display a number of recent blog posts from a specific category. You have the options to choose a title, category, number of posts and whether or not to show the post date or to show the image featured (Post Thumbnails).The posts will be ordered by date just like the default Recent Posts widget included with WordPress. 
check the category you want to show.

Custom Recent Posts Widget Plus

Nice widget it is like the default Recent Posts widget except you can choose a category and in addition show the thumbnails.

Category Teaser vs Custom Recent Posts Widget Plus