What program can print source code well on OS X?
You will find a nice answer over at sister site superuser. It involves a terminal program called enscript which comes with lot's of options and I know at least of one support file for extending its capabilities to print Ruby code.

EDIT:

I just noticed the "clipboard" part of the question. The clipboard content can be accessed from the command line and fed to enscript using pbpaste as mentioned in Matteo answer.