WWW.UBUNTUGEEK.COM just published information on how to download the new set of Bisigi desktop themes for Ubuntu 10.04. These themes build up on the work put together for Ubuntu 9.10 Karmic Koala and represent a strong effort to enhance the Ubuntu desktop looks.
Here are a couple examples of what some of these themes look like:
The Wildshine theme looks particularly impressive here.
These themes add changes to the login page as well as the desktop.
You can learn more about the complete list of themes available and how to download them from this ARTICLE.