Any time the kids get complimented for their behavior, the class earns a fish on the chart. When the chart fills up, I treat them to a compliment reward: a special snack, a pick from the prize box, free time, etc.
I made this so easily. It's actually a car magnet from Vistaprint. I created this image and then uploaded it to Vistaprint's website. And, of course, it was free! That's the beauty of Vistaprint. You usually can get away with only paying shipping costs. I made the fish magnets by attaching different fish stickers to some squares of water-looking scrapbook paper, laminated them, and attached a piece of magnet tape.
The kids love to watch this display fill up and get so excited when they earn compliments. And, honestly, I don't have behavior problems outside of our room, thanks to this little guy.