DasBlog. 

dasBlog Community Edition is an ASP.NET weblogging application. It runs on ASP.NET 1.1 and is developed in C#. dasBlog, an evolution of the BlogX weblog engine, adds lots of additional features like Trackback, Pingback, Mail notifications, full Blogger/M

Here is a testimonial

Another C# based application is .TEXT but it is no longer supported.