What a great thread.
A few years ago, when I was out of work (dang dot-com bust), I spent some time each week volunteering at my synagogue, doing some office work. Eventually I was offered the job for pay, and worked there as a paid member of the office staff for a few months. (Honestly, I would have kept doing it as a volunteer, but they offered to pay me, so why not?) These days, I still volunteer my time, but in a different capacity - I'm redoing their website.
A good friend of mine has deliberately chosen to make service her career. She currently works for a non-profit organization and organizes fundraising events like walks, charity dinners, etc.
It's not about the pay. The pay is usually peanuts. It's about being able to say, "I made the world just a little bit better."