This is one I have been wanting to do for some time, and I have been waiting for my hair to grow long enough: I cut my hair and donated it so that it can be made in to wigs for people who have lost their hair. This organisation/campaign specifically makes wigs for women who have lots their hair due to cancer treatment.
My ponytails are going to the Beautiful Lengths programme in New Zealand, but it is available in many countries.
Apparently I donated my hair before, when I was a child. I don’t remember though: my inspiration for this comes from my then-10 year old sister-in-law who cut her hair off last year for the same reason – what a cool kid!