After a few hours of documenting my code to a satisfactory level, I had a very professional-looking set of HTML documentation. At work the next day, I used Doxygen to generate code for a Visual C# class library, which had been documented with XML comments.
Doxygen supports most C-derived programming languages including C, C++, Java and C#. It also allows you to define custom pages and sections; you are not limited to code documentation.
Documenting a method is very simple: A full list of Doxygen commands is available here.