Microsoft has released a threat modeling tool that allows you to create threat model documents for your applications.
It organizes relevant data points, such as entry points, assets, trust levels, data flow diagrams, threats, threat trees, and vulnerabilities into an easy-to-use tree-based view. The tool saves the document as XML, and will export to HTML and MHT using the included XSLTs, or a custom transform supplied by the user.[1]
[1] Microsoft Website
You can download it here.
David Hayden, Sarasota Web Development