Spatial light modulators (SLMs) form the heart of several current and future optical technologies. These include but are not limited to optical memories, adaptive optics or wavefront correction, active optical elements, femtosecond pulse shaping, neural nets and, of course, optical computing. Over the past 20 years many interestng and technically viable modulators have been developed. However, as none of these areas have yet to breach into high volume consumer markets, affordable high quality SLMs have been euphemistically 'scarce'. The intent of this paper is to assimilate information on a variety of SLM technologies and to explore their advantages and disadvantages, be they real or perceived. We mention several new technolgies; however, the main emphasis is on devices which are currently commercially available.