Scott Hanselman posted a two part series of .NET questions that could potentially be used for interviewing .NET candidates. Although I don't necessarily think they would ensure a well-rounded hire, they definitely include some good technical questions that can help you gauge how deep someone's (and your own) knowledge of .NET is and maybe even help you learn something new:
http://www.hanselman.com/blog/ASPNETInterviewQuestions.aspx
http://www.hanselman.com/blog/whatgreatnetdevelopersoughttoknowmorenetinterviewquestions.aspx
Someone else has already taken the time to answer most of the questions for you. I know, as if you didn't already know all the answers: http://www.ayende.com/Blog/PermaLink,guid,b6e3e8ce-4a6e-4cf0-af70-d360be9e8c76.aspx