Personally, I've been using Python for prototyping. It has lots of lexing libraries, and from there I just do recursive descent. I figure I'll switch to C for a "real" implementation, partly because what I'm going for in my current project is as much database as programming language.

I don't think you have to use C++ to target LLVM. I think you can output LLVM IR from anything and then just call LLVM from the shell to get an executable.