GLS Inc.

This plugin adds featured images (thumbnails) to the default WordPress RSS feed. 
WordPressのデフォルトのRSSフィードにアイキャッチ画像(サムネイル)を追加するプラグインです。
Once activated, featured images will be automatically added to the RSS feed. 
プラグインを有効化すると、自動的にRSSフィードにアイキャッチ画像が追加されます。
This plugin is provided as-is, without any guarantees of functionality or support. 
本プラグインは無償で提供されており、動作の保証やサポートはありません。
Standard RSS Feed URLs: 
– Post Feed: <code>[your-site]/feed/</code> 
– Category Feed: <code>[your-site]/category/category-name/feed/</code> 
– Custom Post Type Feed (example): <code>[your-site]/feed/?post_type=custom-post-type</code>

GLS RSS Thumbnails

Adds featured images to WordPress RSS feeds. / WordPressのRSSフィードにアイキャッチ画像を追加します。

wphigh

Admin Featured Thumbnail WordPress plugin can Add featured image thumbnail to WordPress admin columns. It will help you easy to know which post is attached the featured image. Add click the thumbnail will popup preview the full image.
It also support custom posts.
<a href="http://www.wphigh.com/portfolio/admin-featured-thumbnail-wordpress-plugin" rel="nofollow ugc">Feedback Admin Featured Thumbnail</a>

Admin Featured Thumbnail

Add post thumbnails to admin list of posts.

GLS RSS Thumbnails vs Admin Featured Thumbnail