The first thing I thought of is that I stopped teaching piano lessons. The money was pretty good, but I didn't enjoy doing it. In fact, it felt like a hassle. My husband and I agreed that giving up that income would be worth the benefit for me - not feeling tied down to it, and having to deal with the kids (and parents...) Plus, now I have more time with my own kids!
Funny, but I gave up volunteering for a weekly religion class at my church because I wasn't enjoying it either. I felt guilty about this, but now that you have said this, I realize it was something that has made me happier since quitting.