Custom document type icons/thumbnails
When creating or editing a document type you are able to select an icon and a thumnail image from a dropdown.
The icon will show up in the content section and the thumbnail will be used in the ‘Create Page’ dialog. Giving different document types a different icon/thumbnail is a good way to keep the content section a bit more editor friendly.
It’s also verry easy to add your own custom icons/thumbnails the only thing you need to do is add your images to the folders where these images are stored
Thumbnails:
\umbraco\images\thumbnails
Icons:
\umbraco\images\umbraco
So to add this icon 
to the icons dropdown I just need to copy it into the right directory. Afterwards it will show up in the icon dropdown and I can use this on my document types.
yeah the end result looks really good, although wish it showed icons instead of the drop down list as can never remember the filenames - some great icons here : http://www.famfamfam.com/
cooool