The SparkFun Line Follower Array is an extremely accurate line follower module consisting of eight IR sensors. This Line Follower Arrays was designed to follow a dark line of about 1.5 cm width or smaller (you can spray paint or stick an electrical tape) on a light background. Each array is indicated by a LED.  

The line follower functions by taking an 8-bit reading of reflectance for use with following lines or reading dark/light patterns and can see from about 0.6 to 1.9 cm away. Definitely, this is the ultimate line follower sensor for mobile robot makers and transport automation designers. 

Specifications

• 8 sensor eyes (QRE1113, like in our line sensor breakout).
• I2C interface.
• Adjust IR brightness on the fly with a knob.
• Switch IR on and off with software.
• Invert dark/light sight with software.
• Based on the SX1509 I/O expander

 QRE1113  Datasheet.

Detailed tutorial from sparkfun including arduino connection and code

Detailed tutorial from Geekbot with ready to copy arduino code