Hiring is probably the #1 challenge in Silicon Valley right now. The tight labor market -- especially the top tier -- is affecting both established companies and startups. You can advertise on Craigslist, but I don't know what you'll find. I think you'll have a lot more luck through your personal contacts than by posting job ads looking for strangers.

My guess is that you'll have better luck working your personal network. So, where are you a grad student? You probably know some other students there, right? Have you taught any undergrad courses, where you might have worked with some pretty good students? Have your friends taught any courses? Many times your fellow students can be great partners in this kind of situation, because they're quite motivated and don't have the salary requirements of someone with an established career.

Also, what about your other contacts away from school? Your friends may all be employed, but presumably they will know people who are looking for part-time (or full-time) work.

If you want to hire a programmer for a free, when you'd better try your personal contacts indeed. Otherwise you should try various communities and job sites. Like: Craiflist jobs.37signals.com rubyrockstars.com etc.