Compliments on things I'm insecure about! Kids used to make fun of my smile when I was little so if someone tells me I have a nice smile, my heart grows three sizes.
Probably the best compliment I've gotten while camming are the people who say that they're always smiling in my room, that I've made their bad day better, or some variation about how my happiness has made them happy. It's a really nice feeling to make other people happy, and to know you're entertaining people, and especially from members who have given you lots (in terms of money but also friendship, support, etc). It's just super nice.