I have a "Star Chart" on the classroom's wall and each lesson I give a star to each student if he/she behaves well. This system can also be used to award students for their effort in speaking as much of English as they can or know.
When they reach 10 Stars (bronze stars), I give them a "Bronze Certificate" with a little gift (I use stickers). When they reach 20 Stars (silver stars), they earn a "Silver Certificate" and with 30 Stars (gold stars) they earn the "Gold Certificate".
The students really want to earn the stars, so this system really works (of course, it also depends on the students!).
Here are the 3 certificates (bronze, silver and gold). They are black & white to be printed and copied. To make them more attractive I colour the star afterwards with orange for the Bronze Certificate, grey or silver for the Silver Certificate and yellow or gold for the Gold Certificate.