We do a lot of WordPress installs for clients when we set up new websites for them. One hassle we always go through is setting up the development site as a sub-domain or as a complete other domain, and then having to move it to the new domain. Since WordPress uses absolute URLs in posts, links, etc., editing by hand is definitely not an option. We also couldn’t find a really good solution, so I wrote a plugin that will go through all of your posts, pages, options and guids and update your old domain to your new domain!
This plugin is available for download to be used on your WordPress self-hosted installation.