XmlDocs is a package for Sublime Text 2 & 3 which makes writing documentation makes it easy to write XML-Based documentation. XmlDocs supports C#.
With Package Control installed, you can install XmlDocs from inside Sublime Text itself. Open the Command Palette and select "Package Control: Install Package", then search for XmlDocs and you're done!
Above a variable declaration, function declaration, property declaration, or class declaration, simply type ///<tab> to automatically generate a comment block for the declaration. XmlDocs will attempt to pre-fill in as much information as it can.
To add additional elements, type < to open the autocomplete list of possible tags that can be used.