One of the most common requests I get from IT users of Visio is for a way to draw out an Active Directory topology map. Visio has Active Directory shapes, but until now it didn't have the ability to actually go out and create a diagram from AD. We've put up a free download that does this -- the Microsoft Visio Active Directory Topology Diagrammer is now available. This runs as a separate application and is installed in the Start menu. Here is a screenshot of the UI:

AD diagrammer UI