There might be other themes out there, but these are the ones I know about. Feel free to inform everybody in the comments if you know of any others.

Royale

This theme is really bright and blue… Just look at all that blue…

To install this theme you’ll need to download, extract the zipfile, and then run the installer. When prompted for the location to save the files, leave it set to default.

Now you can go into your display settings and change the theme from the list.

Download Royale Theme from Softpedia

Royale Noir

This theme was supposed to be a darker version of the regular Royale theme, but it wasn’t really finished before somebody from Microsoft published it, and it spread all over the web.

After downloading and extracting the zipfile, you’ll need to copy the royale_noir folder into C:\Windows\Resources\Themes and then double-click on the Luna.msstyles file found in that directory and change the settings to match the above screenshot.

Download Royale Noir theme from istartedsomething.com 

Zune Theme

This theme was released to celebrate the Zune launch, and you’ll notice it’s very similar to Royale Noir, except for the kinda ugly orange start button. Long time readers will note that we’ve mentioned this theme before.

Installing this theme is really simple… download and run the installer.

Download Zune Theme from Microsoft.com