Microsoft research is working on another interesting project which might help us in the future with testing and I am sure you agree that we developers need all the help we can get when it comes to testing.
Although the Pex (Program Exploration) project has been in existence for some time now, the latest CTP release has improved integration with Visual Studio 2008 and a lot more improvements.
In short, PEX learns the program behavior by monitoring execution traces, and uses a constraint solver to produce new test cases with different behavior. You can test your methods (public ones only) without writing one line of code, however once PEX is done with the evaluation you can save the tests as unit tests which are automatically created for you. Other test frameworks are supported through the development of PEX extensions which you can find on codeplex.
Take a look at the introduction video on the PEX web site. Although this project is still in research state within Microsoft Labs it has definite potential and it is worthwhile to keep an eye on it.