Two great things that (could) go great together -- Emacs and Perl talking to each other through a pipe. There's good support for calling in both directions, and the code seems well-thought-out (e.g. circular data structures are properly serialized). I say "could" because the support is incomplete, e.g. hashes can only be passed as opaque references. However, this module's still fun, useful, and fun to use.
Check it out.