I use the Royale,
Royale Noir, and
Zune themes from Microsoft on my computers. I like these because they are free, work without Windows Blinds (these are official Microsoft-released themes), and their bright colors and glassy styling are a huge improvement over the defacto Windows XP Luna theme.
If you want to get Windows Blinds, then you will have to purchase it for $19.95 from their website.
http://www.stardock.com/products/windowblinds/