Discussion sur documentation generator pour C# : http://stackoverflow.com/questions/641364/c-documentation-generator

GhostDoc is a free add-in for Visual Studio that automatically generates XML documentation comments for C# : http://submain.com/products/ghostdoc.aspx

MSDN : XML Documentation Comments (C# Programming Guide) : you can create documentation for your code by including XML tags in special comment fields in the source code. When you compile with /doc the compiler will search for all XML tags in the source code and create an XML documentation file. To create the final documentation based on the compiler-generated file, you can create a custom tool, or use a tool such as Sandcastle.
MSDN : Recommended Tags for Documentation Comments (C# Programming Guide)

Sandcastle – Documentation Compiler for Managed Class Libraries
use the SandCastle GUI tools, SHFB, SandCastleGUI or DocProject which will ease completely the document generation process.

Plus de détail sur Sancastle :
Code project : L’aide contextuel dans Sandcastle
A few faqs about Sandcastle
http://www.codeplex.com/SandcastleStyles MAML Guide / Documenting Web Projects /
Supporting Custom tags in Sandcastle
Documentation des tags