I recently had to move a wordpress site to a totally new domain name. The Backup buddy plugin makes this a breeze, but google (and the other search engines) are still pointing to the old domain name. To redirect users to the corresponding page on the new domain, and to get google to update the url, use the following code in your .htaccess file (you are using apache right?).
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} !newdomain.com$ [NC]
RewriteRule ^(.*)$ http://www.newdomain.com/$1 [L,R=301]
Replace “newdomain.com” with your new domain name, and your users will end up in the right place, and after a little time, the search engines will update your information as well as keep your page ranking that you’ve already earned for all those landing pages.