New URL Mover is a WordPress plugin by thoughtlabllc and lellimecnar that updates your URL in the database automatically when you move your site to a new domain or location.
The plugin will automatically check the location of your installation, and update the database for you if needed. It also adds a widget to your Dashboard to specify the url of your main site.
Download and info: http://wordpress.org/extend/plugins/new-url-mover/