Doubler is a code generator that makes unit testing easier. It is especially useful when working with legacy code. It is a Reflector add-in, a tool already woven into your workflow. It will help you cleave dependencies apart, create test doubles, and write unit tests with little effort and less coding.

Didnt test it jet, but features sound ok.

http://jayflowers.com/doku/doku.php?id=doubler

also added to large tools post:
http://dotnetpret.blogspot.com/2006/04/tools-tools-and-more-tools.html