The DomainTools Whois plugin will automatically link domain names in a WordPress page or blog post to the DomainTools Whois service. It also generates a pop-up containing a summary of Whois information that your visitors can see without leaving your site.

DomainTools Whois Plugin

DomainTools whois plugin shows whois data for domains found in blog articles and links them to whois.domaintools.com.

FasterThemes

Quick Whois WordPress Plugin Shows whois information of the provided domain name. You can use Widget in the sidebar or you can also use Shortcode in the pages/posts.
<a href="http://whois.fasterthemes.com/" rel="nofollow ugc">DEMO of Quick Whois plugin</a>
Features:
<ul>
<li>You can use this plugin in your sidebar by dragging and dropping “Quick Whois” Widget.</li>
<li>You can use this in any specific page/post by putting shortcode [quick_whois].</li>
<li>This plugin converts your website into a whois data provider website in a few seconds !</li>
</ul>
<h3>License and Copyrights for Resources used in this plugin</h3>
i) We have used phpwhois.org php script from this website http://www.phpwhois.org Copyright which is a free software and we are allowed to redistribute it and/or 
modify it under the terms of the GNU General Public License v2.
<pre><code>For any help you can mail us at support[at]fasterthemes.com
</code></pre>

Quick Whois

Quick Whois Plugin Shows Whois information of the provided domain name.  You can do this using Widget/Shortcode.

DomainTools Whois Plugin vs Quick Whois