Applications of Polarization

Polarized sunglasses have their transmission axes oriented to block light reflecting off horizontal surfaces. This light is partly or completely linearly polarized.
Liquid-crystal displays use polarized light. In each segment of an LCD display light passes through a polarizer, through the liquid crystal, and is then reflected to pass back through the crystal and polarizer. Applying just the right potential difference to the crystal rotates the polarization direction by 90^o, so no light emerges and the segment looks black.
Crossed polarizers (polarizers with transmission axes at 90^o to one another) can be used to view stress patterns in plastic models of engineered devices. When light passes through the plastic its polarization direction is rotated. The degree to which it is rotated at each point depends on the stress and on the wavelength of light. White light passing through plastic placed between crossed polarizers produces colorful stress patterns that help engineers determine where the high-stress points are in their designs.
Certain materials (such as calcite) exhibit a property known as birefringence. Birefringent material affects light polarized in a particular direction differently from light polarized at 90^o to that direction; it refracts light polarized one way at a different angle than it refracts light polarized the other way. Looking through a birefringent crystal at something, you see a double image.
The ordinary ray has the same speed in all directions, while the speed of the extraordinary ray depends on direction. For calcite (CaCO₃) we have, in the extreme case:
n_O = 1.658
n_E = 1.486
We don't see this in glass because glass is amorphous - it doesn't have a crystal structure.