I volunteer for Northumbria Blood Bikes. I thought since I give blood and I might need some in a hurry some time that I would put something back and add biking in the mix. The added bonus of riding a full liveried pan or fjr with optional blue lights helps too.
I have found the fundraising aspect quite fun, bag packing and manning a stand at shows and shop entrances. Meeting all sorts of interesting people, spreading the word, showing bikers in a good light. Very worth while.