LANsurveyor Express can automatically create network diagrams for you in Microsoft Office Visio Professional 2007. It’s valued at US$499, but for a limited time, it’s free
LANsurveyor Express for Microsoft® Visio® is a powerful Visio 2007 plug-in that makes it easy to get comprehensive network maps in just minutes! Accessible via the Visio toolbar, LANsurveyor Express automatically discovers your network and produces topology maps in Visio format. Plus, LANsurveyor Express uses Visio SmartShapes® to represent your network devices and populates each node's custom properties with the node's IP address, network name, and fully-qualified domain name.