Does anyone know such a tool?
Both support of "//" and "/* */" is needed.
It'd be nice if it supports aspx-files also.
See the Semantic Designs C# Formatter. The Formatter can pretty-print your code to make it prettier, or fidelity print your code to preserve the way it looks. It has an option to control whether comments are retained or not.
This is probably what you're looking for: Comment Remover
Or you can do this with Replace tool in Visual Studio. Just create proper Regular expression for searching comments