Here is something I am using right now.
It is based on a retrospective technique called 'circles and soup'. It classifies the impediments in two categories: the subject it is dealing with (product, process, people, tools) and the amount control the team has to resolve it.
http://www.futureworksconsulting.com/blog/2010/07/26/circles-and-soup
What I like about is that it gives a nice visualization and can help the team see that they are able to remove impediments by taking direct action themselves or do something to influence or reccomend.
