Hmmm you already mentioned Antlr so I am not sure why you aren't consider it ...
Antlr generates C# (http://www.antlr.org/wiki/display/ANTLR3/Antlr%2B3%2BCSharp%2BTarget) and has an BSD license (http://www.antlr.org/license.html) that seems to have very few restrictions.
Irony (http://irony.codeplex.com/) has quite a number of downloads and a (easy on the eyes) MIT license. Appears to have Full source code so it might be possible to "imbed" this directly into your app.
