Just found this really handy plugin for redirecting a WordPress site. I use it to easily put up a splash page, while working on WordPress in the background.
You basically tell the plugin what URL (or WordPress page) to redirect visitors to, and then allow access to the real site with a users IP address. You can give your client access to preview and train etc, and then when the site is ready to go live, simply turn off the plugin. Saves having to do a migration at the end of development.