Redirects visitors to the the site’s URL as it appears in the WordPress database in case they’re not already connecting through that domain. This is handy for secondary domains that point to your WordPress site.
For example, if example.com and example.net both point to your server, WordPress will normally serve the same site regardless of what the user types in their address bar. 
With this plugin enabled, users visiting the secondary domain will be automatically redirected to whichever domain is configured as the “Site Address (URL)” under WordPress’ “General Settings” page.

Multidomain Redirect

Redirects visitors to the the site's URL as it appears in the WordPress database in case they're not already connecting through that domain.

scideas

<ul>
<li>Find domain name suggestions based on keywords</li>
<li>Find out which suggestions are available, registered and in use</li>
<li>See an image of each possible competitor site found</li>
<li>Click through to register any suggested domains</li>
<li>Configure the number of alternatives for each keyword (paid only)</li>
<li>Edit the suffix list to search for any domain ending (paid only)</li>
<li>Search in your WP admin</li>
<li>Make available to your users via a simple shortcode</li>
<li>siteselector plugin comes with 15 free credits to allow admins to assess it</li>
<li>When credits reach zero siteselector will continue to work at reduced capacity</li>
<li>Use the Buy Credits button to purchase credits for your installation using PayPal</li>
<li>Without credits domain endings cannot be chosen and only one alternative per keyword is used</li>
<li>After purchase your plugin installation will be automatically credited with your purchase</li>
<li>Choose from a range of credit amounts: the more you buy the cheaper they are !</li>
<li>Paid users receive an email reminder when credits are getting low</li>
</ul>

siteselector

siteselector plugin helps you choose a domain name, check it's availability and see your competition

Multidomain Redirect vs siteselector