What are the key chemical structures of liquid crystals used in display technology?

The majority of current flat screen TVs and computer monitors are based on Liquid Crystal displays. 


Liquid crystals are compounds that orient under an applied electric field and alter the polarisation of transmitted light. This can be used to build what are effectively valves that selectively transmit light. 


So what are the typical chemical structures of the chemicals that have these properties and how do the structures relates to how they work?


