The Pololu QTRX-HD-15A Reflectance Sensor Array is great for precisely identifying changes in reflectance (like line detection). It operates from 2.9 V to 5.5 V and offers dimmable brightness control independent of the supply voltage.
In general, the closer the object, the higher the contrast between light and dark readings, but high-reflectance objects are generally detectable out to around 50 mm. This version features high-performance, low-current QTRX sensors with lenses.