ArcVieh

You can select images from media Library in the Widgets backend that will be shown on your Page. You can enter a size for the images.
The thumb-images will be linked to the full-sized-image. 
Requieres PHP 5!

Media Images Widget

Requieres PHP 5! You can select images from media Library in the Widgets backend that will be shown on your Page.

Volkmar Kantor

The plugin provides the functionality to adjust the crop region of cropped images. It add buttons to the edit-pages and media-dialog to access a crop-editor. 
In the crop-editor you can choose one or more (if they have the same ratio) imagesizes and cut-off the part of the image you want.
The plugin is especially useful for theme developers who want to keep full control over cropped image sizes. If you want to dive even deeper, you can get informations about the hooks and filters on the <a href="https://github.com/vollyimnetz/crop-thumbnails" rel="nofollow ugc">github page of the plugin</a>.

Crop-Thumbnails

Amazing work on this plugin. It make developers and users life easier creating a handy-way to crop thumbnails in the used sizes across the site.

Where's the button "This plugin should be native"?

"Crop Thumbnails" made it easy to get exacly that specific image-detail you want to show in your featured image or gallery image.

Media Images Widget vs Crop-Thumbnails