The admin area of a Drupal site should be themed differently according to recent usability research. The idea is that an admin or a content editor needs the context that they are doing admin functions, which an admin theme can provide. The concept of having an admin theme is different for many Drupalers. While numerous Drupal shops have been using them for quite some time, a lot of discussion has focused on using the theme for the site in the admin area. Drupal 7 is embracing admin themes by using one and taking the admin area to a whole new level. But, we don't have to wait for Drupal 7 to have a smoking hot admin theme. Let's take a look at 3 good admin themes for Drupal 6.
Rubik is a theme created by Development Seed and hosted on Github. For it to work properly you, also need the Tao base theme. One of the great things about about Rubik is the icon queues to different actions. Some people think visually and the icons help them do just that.
Seven is the admin theme that ships with Drupal 7. It was designed by Mark Boulton and Leisa Reichelt as part of the d7ux effort. Mike Crittenden back ported it to Drupal 6 so we can use it now. Seven is a very clean and accessible theme.