> This is just off the top of my head, so it may not suit your needs  
> but here goes:  If you happen to use Vim, you could convert the  
> ruby file to an html file with the :TOhtml command, then open the  
> html file in a web browser and print it.  I'm sure that other text  
> editors can do something like this as well.

That's kind of what I was going to recommend. I use a Drupal blog  
with VIM perl modules installed in the blog and on my server to  
syntax color code, ruby included.

  - Ken