Rewarding Good Behavior

I know that it is beneficial to reward students for good behavior, it's a good incentive for them. My current system rewards the entire class if they've done well. I've done this because it seemed overwhelming to try and have a system to reward individual students when I have over 500 of them.
I've been looking for something new though because right now I reward the class with a sticker for a good class period and 5 stickers gets them some free art time at the end of class. The problem here is that I am giving up class time so they can have free time. It messes up lesson plans, puts some classes behind, I forget about it, etc.
I recently learned about another art teacher's reward system. He gives stars to individual students with good behavior, and he only gives out 4 stars at the end of each class. Once a student has accumulated enough stars they can come to his room at the end of the day to pick a small prize.
I think I will try this next year. There are several things I like about it. It doesn't affect class time, the students are responsible for remembering to come to the art room for a prize (not me trying to remember), the entire class is not punished for the actions of a few, and it recognizes good students. I sometimes feel that I pay more attention to the students who misbehave or are having problems and I barely notice the quite well behaved ones. This kind of a system would challenge me to keep my eyes open for those students who go above and beyond; the helpers, those who clean up quickly, who listen well, etc. And it won't take any more time to put down 4 stars at the end of class than it does now to pick a student to put a sticker on the chart.
Do you have a system for encouraging students to follow rules and have good behavior? What works and doesn't work for you?