This is old news but I wanted to make sure that I keep a link to it.

Mike Stall wrote a C# compiler called “Blue” (download)  back in 2001.  Here are fast facts listed on his post:

- It’s written 100% in C#.

- It uses Reflection to import all references and Reflection.Emit to emit the IL.

- Everything (particularly the parser and lexer) were written by hand.

- It has the standard compiler pipeline as described in the dragon book.

- It produces verifiable IL (you can run PEVerify on the output and it passes).