Androfire

TDisplays links from del.icio.us, Technorati, Reddit, Digg and TailRank that is relevant to the current category of your blog. Eg: Your visitor browses the ?humor? category of your blog; the links will come from ?http://del.icio.us/tags/humor? and so on. This means that you do not have to change any code for each specific category.

WP-ExternalFeed

Displays links from del.icio.us, Technorati, Reddit, Digg and TailRank that is relevant to the current category of your blog

MailerLite

This plugin automatically adds featured images of your posts into the RSS feed.
Features:
<ul>
<li>Automatically adds featured images of your posts into the RSS feed</li>
<li>Choose from all available image sizes</li>
<li>Choose from multiple image alignment options</li>
</ul>

Featured Image in RSS Feed by MailerLite

This plugin automatically adds featured images of your posts into the RSS feed.

WP-ExternalFeed vs Featured Image in RSS Feed by MailerLite