If you have a MOSS 2007 environment, it is easy to create a Site Directory Site using the template... it is commonly used for cataloging sites, or some time served as sitemap in many organization...
Other day I was tasked to create Site Directory site in SP 2010...but the template is disappeared in SharePoint 2010... With some research. I come across a posting by Usman Afzal... the feature was hidden in SharePoint 2010, it require a few steps to re-activate the template.
Check this link for more details instructions.
Hope this help.