in C# I have a string I am writing to the outputstream of the response. After I save this document and open it in Notepad++ or WordPad I get nicely formatted line breaks where
Yes - it means you're using \n as the line break instead of \r\n. Notepad only understands the latter.
(Note that Environment.NewLine suggested by others is fine if you want the platform default - but if you're serving from Mono and definitely want \r\n, you should specify it explicitly.)