sorry, by the time I read and posted, a few people put responses in.
Results in 302
Code:
Redirect / http://www.domain.com/
Results in 302
Code:
<?php
header("Location: http://newsite.com/");
?>
Results in 302
Code:
ErrorDocument 404 http://newsite.com
Results in 301
Code:
RewriteEngine on
RewriteRule .* http://domain.com/ [R=301,L]
h20neil's suggestion of parking a domain on another, or overlaying, will also work. The problem there is that google could see both domains serving the same content and knock one out for the dupe page penalty.