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
An LL(1) pull parser and generator that thinks it's an LL(k) parser - with a rich, simple and beautiful EBNF syntax
Using Parsley to parse a C# subset into the CodeDOM
Generate powerful, maintainable parsers in most major .NET languages using a friendly grammar format
Using PCK to create grammars, parsers and tokenizers for C# and other .NET languages
A parser generator and unification system for different parsing tools
Using PCK's grammar system, and understanding the concepts behind it
An LALR(1) parsing algorithm as part of Pck
A Pike VM for running non-backtracking NFA regular expressions in C#
Getting an accurate CodeDOM back from a C# source subset