This is a prototype for a museum exhibit that would use printed cards with black and white squares to encode a number onto each card. Software would read the card and facilitate game play.
SparkFun Line Sensor Breakout - QRE1113 (Digital)
The QRE1113 breakout board features a digital output, using a capacitor discharge circuit to measure the amount of reflection. This tiny board is perfect for line sensing when only digital I/O is available, and can be used in both 3.3V and 5V systems.
Any Arduino works... I prototyped with an Arduino UNO.