A Drupal 6 rip of the new D7 theme "Bartik".
Using the XSL Engine and being a sub-theme of XSL Absolute starts XSL Bartik off with a lot of power behind it. With the page, node and comments already looking great thanks to the creators of Bartik you have a great looking site from the get-go. Then by using the power of XSLT in your theming engine allows you to customize easily and elegantly.
http://drupal.org/project/xsl_engine
http://drupal.org/project/xsl_absolute