If you use the CodeDOM, here's an indispensable package to make it awesome.
A completely programmable lexer/tokenizer/scanner generator in C# using a Pike Virtual Machine
Using Parsley to parse a C# subset into the CodeDOM
Use the Parsley compositional parser generator to parse a complicated grammar with backtracking.
Generate powerful, maintainable parsers in most major .NET languages using a friendly grammar format
Make your projects far more powerful with some foundational code templating techniques
A simple helper class to aid in code generation
Parse, analyze, and transform your code with Slang
Build a full featured tokenizer generator in C#
Generate fast, easy to use lexers/scanners in major .NET languages