Zby has a great idea. If you fix bugs in big open-source projects, can't you get some reputation / whuffie in a physical format (eg. a letter that you can take to a job interview.)
Of course, if you're interviewing at a decent company, and you have some visibility within an open-source community, you should be able to point them at it anyway. But this could be useful for cases where your contributions are valuable but obscure and the potential employer not so clued-in.