Here is how the old icon appears:

With the new icon:

Here is a link to a .zip file containing the the images.
http://jpkvideo.com/geektool/GTmenuIcons.zip
They get placed in 'GeekTool.prefPane/Contents/Resources/GeekTool.app/Contents/Resources'.
Here is a link to an installer which will automatically replace the icon.
http://www.jpkvideo.com/geektool/GTMenuIcon.dmg
Hopefully if the author likes this icon it will be included in future releases.