It's a slightly strange way to release it, admittedly, but if you're bored with the standard blue, silver and green variants of the Luna theme that ships with Windows XP, you can now download the Royale / Energy Blue theme. This theme originally shipped with Windows XP Media Center Edition, but Microsoft New Zealand have now released it in a form that can be installed on Windows XP Professional and (I assume) Windows XP Home Edition. It's the best dressed you've seen Windows XP - it looks like a more professional version of Luna Blue, with more subtle hues. It also confuses the Office 2003 theming system sufficiently that it doesn't attempt to impose its own somewhat garish (to my taste) color scheme.
Thanks to Jeff Sandquist for the link.