This paper proposes a unified operational value index of energy storage in the smart grid electricity market environment. Given the heterogeneity of many storage service providers enabled by smart grid technologies, this unified value index will allow for comparison across different technology choices. It is also argued that implicit forms of energy storage, such as demand response, should be valued and utilized. A cross-market cooptimization is proposed to maximize the operational value of energy storage under the deregulated electricity market environment. For numerical illustration a case study is conducted in a modified 24-bus IEEE Reliability Test System (RTS), which includes flywheels, battery storage in the form of plug-in electric vehicles, and price responsive thermal load.