A widget that simply gives you related posts by taxonomy. Four settings to customize the widget: title, taxonomy, related posts count, excludet terms
You are wellcome to ask questions directly to me in the Simply-Related-Posts-section on my blog http://www.danielauener.com/simply-related-posts/
There is even a github-repository on: http://github.com/danielauener/wp-simply-related-posts
Q. How to add thumbnail images to the related posts list A. You can add the 'simply_related_posts_title' filter, like
add_filter( 'simply_related_posts_title', 'my_related_posts', 10, 2);
The first argument is a post-object for the related post, the second argument is the widget instance.