Skype Voice Changer
http://skypefx.codeplex.com/

Skype Voice Changer demonstrates how to use NAudio and Skype4COM to allow real-time effects processing of your voice during a Skype conversation. It is developed in C#. Eventually, it is intended that the effects framework in this project will become part of the core NAudio library. This has been aded to the tools section of Research Resources Subject Tracer™ Information Blog.