Windows media Center 2005 shipped with a unique theme called Royale. This is the theme I use on my desktops. Last week someone posted a download to another, unreleased variant of the Media Center theme. The secret theme is very black and called Royale Noir. Read more about it at istartedsomething.com.
You can download it here.
To install: Extract files to “c:\windows\resources\themes\royale noir” and double click on “luna.msstyles”. Select “Noir” from color scheme. Code-signed by Microsoft. No UXTheme hack required.