Peadig

rel=”external” is now the XHTML valid version that informs search engine spiders that the link is external. However, using this does not open the link in a new window. target=”_blank” and target=”_new” does this, but is not XHTML valid.
This very simple plugin adds a small JS file to your header to let this happen!
<ul>
<li><a href="http://pleer.co.uk/wordpress/plugins/rel-external/" rel="nofollow ugc">rel=”external”</a> plugin homepage.</li>
<li>More <a href="http://pleer.co.uk/wordpress/plugins/" rel="nofollow ugc">WordPress Plugins</a>.</li>
<li><a href="http://pleer.co.uk/wordpress/plugins/facebook-comments/" rel="nofollow ugc">Facebook Comments</a> Plugin</li>
<li><a href="http://pleer.co.uk/wordpress/plugins/wp-twitter-feed/" rel="nofollow ugc">Twitter Feed</a> Plugin</li>
<li><a href="http://twitter.com/alexmossSEO" rel="nofollow ugc">Follow @alexmossSEO on Twitter</a>.</li>
<li><a href="http://alex-moss.co.uk/" rel="nofollow ugc">Alex Moss</a>.</li>
<li><a href="http://pleer.co.uk/" rel="nofollow ugc">Pleer SEO</a>.</li>
</ul>

rel=”external” in a New Window

Opens a new window with rel="external" instead of having to use target="_blank" or target="_new"

keith graham

The Open in New Window Plugin Plugin uses JavaScript to target external links to a new browser window, leaving your blog page open. 
Since it uses javascript, it targets more links than using a plugin that filter pages and rewrite the link. The plugin will find many links generated in scripts or pasted into posts and comments. 
Due to the limitations of javascript it will not be able target links in iframes such as Adsense and some other affiliate links.
<h3>Support</h3>
This plugin is free and I expect nothing in return. If you wish to support my programming, buy my books: 
https://linktr.ee/keithpgraham

Open in New Window Plugin

Works for me

Opens external links in a new window, keeping your blog page in the browser so you don't lose surfers to another site.

rel=”external” in a New Window vs Open in New Window Plugin