Jorge A. Gonzalez

Easy External Links is a SEO friendly, external link handler for WordPress.
The current aim of Easy External Links is to standardize the format of external links and create consistent on-page SEO.
<a href="http://watchworthy.io/underwater-base-jumping/" rel="nofollow ugc">Demo</a> | <a href="https://s.w.org/plugins/wp-links/screenshot-1.png" rel="nofollow ugc">Options</a>
<h3>Features</h3>
<ul>
<li>Open external links in a new tab or current tab</li>
<li>Domain Filtering</li>
<li>Show icon next to external link (100 icons to chose from) </li>
<li>External image hosting support</li>
<li>Add rel=”external nofollow” to external links</li>
<li>Add title attribute to external links (uses to the text of the link)</li>
<li>Add target=”_blank” to comment links (rel=”external nofollow” coming soon) </li>
<li>Add target=”_blank” to external links in excerpts</li>
</ul>

Easy External Links

Install, activate, configure, forget. Works really well!

As simple and as good as it gets

Take control of external links in WordPress posts, pages & comments. Insert rel=external nofollow and target=_blank to all your external links.

Erin McIntyre

This plugin searches links on your site for the domain that you specify in the settings, adds your affiliate ID, and makes those links open in a new tab when clicked.
The plugin produces XHTML Strict compliant code and is search engine optimized (SEO). 
This is done using JavaScript’s <code>window.open()</code>-function. It adds only a few lines of vanilla JavaScript to the page, and does not require any external libraries like jQuery.
Most other plugins perform a hack by altering the <code>target</code> parameter (i.e. <code><a href="http://somewhere.example" target="_blank"></code>). That method is not XHTML Strict compliant.
This plugin handles the links client-side, which lets search engines follow the links properly. Also, if a browser does not support JavaScript, the plugin is simply inactive, and does not result in any errors.
Credits 
Inspired by the <a href="https://wordpress.org/plugins/open-external-links-in-a-new-window/" rel="ugc">External Links in New Window / New Tab</a> plugin.
Known bugs 
The plugin conflicts with other plugins that change the links’ `onClick´ attribute.

Easy External Links vs Affiliatize Me