PResponsive

This plugin will add a image below your posts, allowing your visitors to share your posts with their friends, on FaceBook, Pinterest, Google+, Twitter, Myspace, Friendfeed, Technorati, del.icio.us, Digg, Google, StumbleUpon, and other. After plugin is activated a buttons will appear after the content of the post.Clicking this button will bring the user to the bookmarking site. If the user isn’t logged in they will be prompted to do so. 
Post your articles to the social bookmarking sites and get traffic.

WP Social Bookmarking

WP Social Bookmarking plugin syndicates your blog posts in social networking sites.

brasofilo

The plugin adds a meta box where you can upload or select an image from your media library.
After selection, the default Link Image field is populated with the image URL and a preview is available in the meta box.
The plugin also adds a Thumbnail column in the page /wp-admin/link-manager.php
Inspired by <a href="http://wordpress.stackexchange.com/questions/44902/uploading-images-for-links" rel="nofollow ugc">this question</a> in WordPress Answers.
<h4>Localizations</h4>
Português & Español

Featured Link Image

Add a meta box in the Links add/edit page for easy uploading/inserting images in your bookmarks.

WP Social Bookmarking vs Featured Link Image