[simon_weber]

The same advice applies for undergrads (though I wouldn't call myself a mentor). For a year or two now I've been part of a group of students who hold volunteer CS "office hours". We normally get visits from frustrated students who aren't in CS, and are able to make a huge difference for these people.

We don't get paid, but I still benefit from it, of course; my knowledge and teaching ability have both greatly improved. It's fun, too =)

A word of advice: operate outside of your school's official tutoring system. Just get a bunch of friends and make yourselves known within your department: you'll spend less time working the system and more time helping people. Feel free to get in touch for advice.