It will be now one year I've been involved in Software Carpentry. One of the great thing about it is that I got to meet (mostly online) a lot of great people. That's how I discovered “paper clickers”.
What is a clicker? It is just a device that allow a student to vote in live to answer a question. Paper clickers are an embarrassingly cheap version of electronic clickers. It allows me, as a teacher, to gather instant feedback on what students understand. Believe me, this is a game changer, but I'll talk about this and how I easily put quizzes in my slides… but later. This page explains the principle well.
As I like to have control on my tools, I made my own clickers. It is meant to be printed double sided and each sheet is meant to be cut in two (it contains two clickers). It is perfectly aligned for the printer I used. I provide the PDF file so that you can use it. If you really want perfect alignment, I can share my calibration procedure, just ask me.
If you use it, please let me know how it went, I'd be very interested.