We've been experimenting with Pex (Program EXploration) which produces a traditional unit test suite with high code coverage. These generated unit test cases takes parameters, calls the code under test, and states assertions. Essentially, Pex does a white box program analysis and provides higher code coverage. 

Per Peli de Halleux's blog,  major highlights of Pex Version 0.9 release are: Pre-Release license for Visual Studio 2008, better test framework integration and partial support for Visual Basic.NET/F# (read the full release notes)

Other References and download URLs of Pex:

Nikolai Tillmann's Blog

Pex – Automated White Box Testing for .NET

http://msdn.microsoft.com/en-us/devlabs/cc950525.aspx

http://research.microsoft.com/en-us/projects/pex/