Aaron Johnson investigates how to produce xml documentation for C# without using Visual Studio:

the C# compiler will then strip our your comments, package hierarchy, related classes and create an xml file, in the above case, called 'MyClass.xml'. In and of itself, this doesn't do you much good. But if you download NDOC from sourceforge, you can create not only Microsoft MSDN style help files, but JavaDoc help files, LaTex helps files and plain xml.

I've been using Scite to write C# recently. You can easily customise the build command for .cs files. I'm running a NAnt build script that builds the project, builds the NUnit tests, runs the tests, and commits changes to CVS if the unit tests all pass. Fun, and it makes TDD dead simple.