Microsoft Active Directory Topology Diagrammer
In case you are not familiar with this tool, this is worth checking out. The Microsoft Active Directory Topology Diagrammer reads an Active Directory configuration using ActiveX Data Objects (ADO), and then automatically generates a Visio diagram of your Active Directory and/or your Exchange 200x Server topology. The diagrams include domains, sites, servers, administrative groups, routing groups and connectors and can be changed manually in Visio if needed.
The tool works on Windows 2000/2003/XP/Vista. You can download the tool here.