WiredBot is one of the only IRC bot's for the Win32 platform! It features scripting, multiple channels, and a nice GUI! WiredBot uses SmartIrc4net's .NET class library for IRC. It is licenced under the LGPL and is writen by Mirco Bauer.
Thresher is a .Net IRC client library designed to serve as the basis for IRC bots and GUI clients. It is written in C# but can be used by any .Net supported language. Thesher also works with Mono on Linux.
MYrc is an IRC GUI client (similar and probably (more like definately) based on Mirc, hence the name) written in C# made possible with the Thresher IRC Library. It had a Plugin Architecture allowing to easily write plugin in C#.