Everaldo Canuto

Using this plugin you can heve different URL’s for your WordPress frontend and 
backend.
<h4>Credits</h4>
This plugin is created by <a href="https://twitter.com/ecanuto" title="Everaldo Canuto" rel="friend nofollow ugc">Everaldo Canuto</a> with sponsorship from <a href="http://nuveo.com.br/" title="Nuveo" rel="friend nofollow ugc">Nuveo</a>.

WP Domains

Just works

Use different domains for backend (admin) and frontend on Wordpress.

Nimbus Digital

Redirects http://somedomain.tld to http://someotherdomain.tld
Assuming you have 2 or more domains in use for a single WordPress site. This plugin forces the use of only one no matter which is entered in the address bar.
If, for some reason, your host won’t automatically redirect from one domain to another, then this plugin will do it. It checks the URL used to access the site and does a 301 redirect if incorrect.
In theory htaccess should do this, but in my case it didn’t. Perhaps because I am using domain aliases (or CNAMEs) and I wanted to insure that the main one was always in use, even when accessed using old links.

Force Domain Redirect

Forces your Wordpress site to load on the domain registered in the WP admin.

WP Domains vs Force Domain Redirect