CsLex

A lexical analyzer generator for C#
http://www.cybercom.net/~zbrad/DotNet/Lex/

ANTLR

 - Powerful paring engine supports lexical token parsing, rich grammar rules and very interestingly (and usefully) parse tree parsing. Although you'll need a Java JDK 1.4 to run it, it can be used to generate C# source code.
" ... provides a framework for constructing recognizers, compilers, and translators from grammatical descriptions containing Java, C#, C++, or Python actions."