Static Image Widget
With all the same features as the Featured Image widget, the Static Image widget allows you show a specific image in any widget area, (including the full window width).
Additional widget features:
Manually set image
The widget uses the standard WordPress media library so you can select an existing image or upload a new one.
Set your own text
Rather than using the post title and excerpt, the Static Image widget allows you to enter your own text.
Read about the other features on the Featured Image widget page.