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"

Nicki Faulk

This plugin marks all links in posts as ‘external’ and implements a small bit of javascript to open links in new windows. Inspired by Mdkart’s Add Lightbox plugin.

Blank Target Replacement

A target=_blank replacement using a small piece of javascript and rel=external.

rel=”external” in a New Window vs Blank Target Replacement